|
ANDHRA PRADESH CODE OF TECHNICAL INTERFACE Section 3 CONNECTION CODE |
Table of Contents
|
3.1.1 Users |
|
3.1.2 Licensee |
|
3.1.4 Data from APTRANSCO |
|
3.1.6 Acceptance or Rejection |
|
3.1.7 Connection Agreement |
|
3.1.8 Data Exchange |
|
3.1.9 Non-Acceptable Offers |
|
3.2.2 Objectives |
|
3.2.3 Connection Agreements |
|
3.2.4 Connection Site Matters |
|
3.2.6 Connection Point |
|
3.2.7 Data Requirements |
|
3.4.1 Introduction |
|
3.4.3 Implementation |
|
3.4.4 Voltage Criteria |
|
3.4.5 Frequency |
|
3.4.6 Reliability Criteria |
|
3.4.7 Harmonic Distortion |
|
3.4.8 Voltage Flicker |
|
3.5.1 General Principle |
|
3.5.2 Safety |
|
3.5.3 Insulation |
|
3.5.4 Clearances |
|
3.5.5 Earthing |
|
3.5.6 Safety Training |
|
3.5.7 Motor Starting |
|
3.5.8 Access to APTRANSCO |
|
3.5.12 Power Factor |
|
3.6.1 Introduction |
|
3.6.2 Objective |
|
3.6.3 Procedure for Number and nomenclature of plant and apparatus at connection sites |
|
3.7.1 General Principles |
|
3.7.2 Fault Clearance Times |
|
3.7.3 Protection Requirements |
|
3.8 Earthing |
|
3.10 Operational Metering |
|
Appendix-B Specifications of Under Frequency Relays |
3.1 Procedure For Application For Connection
3.1.1
Users
Any User
seeking to establish new or modified arrangements for Connection to and/or use of the Transmission System
shall follow the procedures laid out in this Code.
3.1.2 Licensee
The Licensee
(APTRANSCO) shall follow the
procedures and time limits specified in this Code in processing the
application, making or modifying an offer and rejecting an offer.
3.1.3 Optimal
Connection Locations
APTRANSCO shall publish annually before 31st March, a list of
points which are technically optimal connection locations where generators and
suppliers can connect their systems to APTRANSCO system.
Any prospective user or existing user wishing capacity
enhancement may after studying the Long Term Plan and the Statement of
Opportunity published by APTRANSCO may request APTRANSCO for more information.
APTRANSCO shall furnish the data equired within 15 days of requisition. APTRANSCO may refuse to furnish the data if
it considers the data is confidential and is not required for the business of
the prospective user. APTRANSCO may
charge reasonable cost for supplying the data.
3.1.5
Application for Connection
Any User seeking use of the Transmission system may
submit an Application for connection to APTRANSCO in Format developed by
APTRANSCO.
APTRANSCO shall either accept or reject the application
within 30 days from the date of
Application. If rejected, APTRANSCO
shall communicate the reasons. If APTRANSCO requires additional data from the
Applicant the last date for acceptance or rejection may be extended by another
month from the date of submission of the additional information. The additional
data shall be furnished to APTRANSCO within 15 days from the date
requisitioned. If the additional information is not received by APTRANSCO
within 15 days, it can either reject the Application or extend the date.
If the Application is accepted then APTRANSCO and the
user shall proceed to finalise a Connection Agreement as per para 3.2.3.
The data exchange between APTRANSCO and users shall be
in accordance with the provisions of the Planning code.
In the event of the offer becoming invalid or not
being accepted by any User within
the validity period, no further action shall be taken by the APTRANSCO on the Connection applications.
3.2 Connection Conditions
3.2.1 Introduction
Connection
Conditions specify the technical,
design and operational criteria which must be complied with by any User connected to the Transmission System.
3.2.2 Objectives
The objective of
this Section is to ensure the following:
(i)
All Users or prospective Users are treated equitably.
(ii)
Any new Connection shall not impose any adverse
effects on existing Users, nor shall
a new Connection suffer adversely
due to existing Users.
(iii)
By specifying minimum
design and operational criteria, to assist Users
in their requirement to comply with License
obligations and hence ensure that a system of acceptable quality is maintained.
(iv)
The ownership and
responsibility for all items of equipment is clearly specified in a schedule
(Site Responsibility Schedule) for every site where a Connection is made.
3.2.3 Connection Agreements
A Connection Agreement shall be drawn up specifying the general conditions
for connection and any specific conditions, both technical and financial,
applicable to that connection.
If the design
parameters based on which the original offer was made, have changed, APTRANSCO shall
make a revised offer to the User including revised terms and extended time
limit for submission of data. This revised offer shall form the basis of any
Connection Agreement.
3.2.4 Connection Site Matters
3.2.4.1 Site Responsibility Schedule
For every Connection
to the Transmission System for which a Connection Agreement
is required, a schedule of equipment shall be prepared by APTRANSCO with information supplied by the respective Users.
This shall include:
·
Schedule of HV
Apparatus
·
Schedule of
Plant, LV/MV Apparatus, services and supplies
·
Schedule of
telecommunications and measurements Apparatus
·
The safety rules
which apply to each Plant/Apparatus
A Site responsibility Schedule, shall state the
following for each item of equipment installed at the Connection Site:
(i)
The ownership of
equipment.
(ii)
The
responsibility for control of equipment.
(iii)
The
responsibility for maintenance of equipment.
(iv)
The
responsibility for operation of equipment.
(v)
The manager of
the site.
(vi)
The
responsibility for all matters relating to safety of persons at site.
(vii)
The
responsibility for all matters relating to safety of equipment at site.
All H.V. Apparatus on any connection site shall be shown on one diagram which shall include details of the following.
1.
Bus bars
2. Circuit Breakers
3. Isolators
4.
Bypass facilities
5.
Earthing switches
6.
Maintenance of
Earths
7.
Overhead line
entries
8.
Overhead line
tappings
9.
Cable and Cable
Sealing ends
10.
Generating Unit
11.
Generating Unit
Transformers
12.
Generation unit
auxiliary transformers including lower voltage circuit breakers
13.
Station Service
Transformers including lower voltage
circuit breakers
14.
Capacitors
including synchronous compensators
15.
Series and shunt
reactors.
16.
Grid Transformers
(Inter Connecting transformers)
17.
Tertiary windings
18.
Earthing and
Auxiliary Transformers
19.
3f Voltage transformers
20.
1f Voltage transformers with phase identity
21.
Surge Arresters
22.
Neutral earthing
arrangements on HV plant
23.
Current
transformers
The User
owning the Connection site shall
provide reasonable access and other required facilities to another User whose equipment is installed at
the Connection site for
installation, operation and maintenance, etc.
Each Connection point shall be precisely shown.
An illustrative Site Responsibility Schedule is
provided in the Appendix to this Section.
Site Common Drawings shall be prepared by the owner
Company (APTRANSCO or Users) using the information furnished by the other
Company (User or APTRANSCO) containing the following information:
(i)
Connection Site
Equipment layout
(ii)
Electrical Layout
(iii)
Common Protection
and Controls
(iv)
Common Services.
SCDs are updated by the request and initiation of
either company but the responsibility of updating at every change lies with the
site owner.
3.2.4.3
Maintenance at Connection Site
The User’s equipment at the APTRANSCO’s site shall be maintained promptly and properly by the User and vice versa so that the equipment and personnel of the site owner are not jeopardised by the neglect of the other Company.
3.2.4.4 Site
Operational Procedures
APTRANSCO and User must make available staff to take
necessary safety procautions and carryout operational duties at the Site. The
written operating and safely instructions must be available at the site.
3.2.5 System Performance
(a)
All equipment
connected to the Transmission System
shall be of such design and construction as to satisfy the requirements of the
relevant Indian Standard Specification.
Where no BIS exists, the appropriate IEC Standard or equivalent International Standard will apply.
(b)
Installation of
all electrical equipment shall comply with IE
Rules
(c) For
every new Connection sought, the APTRANSCO shall specify the Connection
Point and the voltage to be used, along with the metering and protection
requirements as specified in the Metering and Protection Sections.
(d) The Transmission System frequency shall be
in accordance with the Grid Characteristics Section. The User shall however be subject to the grid discipline prescribed by SLDC/ SRLDC as per guidelines mutually
agreed with SREB/ SRLDC.
(e) Voltage
variation on the Transmission System shall
be in accordance with the Grid Characteristics Section.
(f) Insulation
co-ordination of the Users’
equipment shall conform to applicable Indian Standards/Codes. Rupturing
capacity of switchgear shall not be less than that specified by APTRANSCO.
(g) Protection
and Metering schemes shall be as detailed in the Protection Section of the Code.
For existing Power
Stations, the equipment for data transmission and communications shall be
owned and maintained by the APTRANSCO, unless alternative arrangements are mutually agreed.
For new Power
Stations the equipment for data transmission and communications shall be
owned and maintained by the respective Generator.
(h)
The new
Generating units to be connected to the Grid shall be capable of increasing the
output by 5% instantaneously upto 105% MCR for a minimum of 5 minutes.
(i)
The new
Generating units shall have AVR and turbine speed governor with overall droop
of 3 to 6%.
3.2.6 Connection Point
3.2.6.1 Generator
Voltage may be 400/220/132 kV or as agreed with the APTRANSCO.
Unless specifically agreed with the APTRANSCO:
·
The Connection Point shall be the first
takeoff tower from the Power Station switchyard which is the boundary
between GENCO and APTRANSCO
The Tariff Metering Point shall be between the
synchronising breaker and the EHT bus on
the HV side of the Generator Transformer, or each feeder, i.e.,between the
feeder breaker and the line isolator of the feeder.
All equipment, including metering, protection and
communication up to the GENCO-TRANSCO boundary shall be maintained by the Generator, and all equipment beyond the
Boundary (towards the line) shall be maintained by APTRANSCO.
3.2.6.2 Distribution
Company
Voltage may be 33/11 kV or as agreed with the APTRANSCO. All 33 kV lines and below shall be under the
jurisdiction of the DISCOMs. All
lines and network above 33 kV shall be under the jurisdiction of APTRANSCO.
·
The Connection Point shall be the first take off pole of the 33 or
11 kV feeder which is the boundary between APTRANCO and DISCOMs.
Alternatively the outgoing terminals of the Line Isolator of the 33 kV
or 11 kV Feeder.
·
The Tariff Metering Point shall be between the
All equipment, including metering, protection and
communication on the transformer side of the Boundary shall be maintained by APTRANSCO, and all
equipment beyond the Boundary shall be maintained by DISCOMs.
All HT services including EHT services such as 132 kV
and 220 kV shall be with DISCOMs as
per geographical jurisdiction.
3.2.6.3 CPPs
& Bulk Power Consumers
Voltage may be 220/132/33 kV or as agreed with the APTRANSCO.
Sub-stations are owned by CPPs and Bulk Power
Consumers. The Connection Point
shall be the feeder gantry in their premises.
3.2.7 Data Requirements
Users shall provide the APTRANSCO with data
for purposes of this Section as
specified in the Annexures to Planning Code and as requisitioned by APTRANSCO.
The DISCOMs shall install low frequency relays at various locations to shed load when frequency falls. APTRANSCO and DISCOMs shall enter into Agreements regarding the amount of load in MW to be shed at different values of low frequency. The location at which loads are to be disconnected shall be decided by the DISCOM. The specifications of the low frequency relays are given in Appendix B. The LT AC power supply to the Low Frequency Relays shall be derived from the primary supply i.e, Station Auxiliary Transformer but not from the external public distribution system.
3.4 Grid Characteristics
3.4.1 Introduction
This section specifies the electrical parameters of
performance of the GRID which affect the performance of connected Users and
other transmission systems interconnected with the AP Transmission Grid.
3.4.2 Objective
(i)
To ensure that
the GRID performance meets a minimum standard which is essential for the Users’
system and equipment to function properly.
(ii)
To enable Users
to design their systems and equipment to suit the electrical environment that
they operate in.
(iii)
To enhance the
quality standards of the AP Electrical System towards standards stipulated in
or established under the authority of National and State Acts and Rules in the
short term and gradually moving towards international standards in the long
term.
3.4.3 Implementation
The GRID performance standards established herein shall be implemented in a manner so as to ensure that no entities are forced to achieve goals beyond the capability and limitations of the current system in the immediate future while continuing to strive for the higher standards by improving their system in the long term.
To this end, the CTI shall be implemented in three
Stages:
Preliminary Stage:
The time period immediately following approval of the first version of the CTI by APERC. Existing conditions to prevail. However all entities shall endeavour to minimise the duration of the Preliminary Stage.
Transition
Stage:
An agreed time period during which improvements are made to the system with the injection of investment capital.
Final Stage:
An agreed time
period when substantial improvements have been carried out and the
system is considered to be in satisfactory condition with the needed capital
investment.
Standards for different Stages will be different.
The length of the Preliminary Stage and Transition
Stage shall be determined by the Regulator who will inform all parties
concerned of impending change to the next stage at least six months in advance.
3.4.4
Voltage Criteria
The voltage criteria
detailed below are the target values to be achieved under the leadership of APTRANSCO, in coordination with
SRLDC and with the cooperation of the Power Sector Utilities in
3.4.4.1 Voltage Variations (CEA Standards)
|
System Voltage |
Maximum (RMS) |
Minimum (RMS) |
|
400 kV |
420 kV |
360 kV |
|
220 kV |
245 kV |
200 kV |
|
132 kV |
145 kV |
120 kV |
3.4.4.2 Voltage Unbalance
The
phase voltages of a 3-phase supply should be of equal magnitude and 120o
apart in phase angle. Deviations will result in decreased efficiency, negative
torque, vibrations and overheating. Severe unbalance could lead to
malfunctioning of some equipment. Voltage unbalance is defined as:
Voltage Unbalance = Deviation between highest and lowest
phases
Average voltage of three
phases
Limits
for voltage unbalance are:
220kV
and above: 2%
Below
220 kV: 3%
Balancing loads on individual phases will help greatly in avoiding unbalanced voltages
3.4.5 Frequency
Frequency of the
transmission system should be maintained within an acceptable range to ensure proper operation of the system. Insofar as possible,
APTRANSCO shall fulfil its parrtial responsibility to enable SRLDC to keep the
frequency within acceptable ranges and avoid the periods where the frequency
values given under “Extreme Conditions” prevail.
TABLE
Frequency Limits
|
SREB Standards : “targets” to be achieved: |
|
|
Upper limit: |
50.5 Hz |
|
Lower limit |
49.5 Hz |
|
|
|
|
Statutory Limits : acceptable |
|
|
Upper limit: |
51.5 Hz |
|
Lower limit: |
48.5 Hz |
|
|
|
|
Extreme Conditions: |
|
|
Upper limit: |
52.5 Hz |
|
Lower limit |
47.5 Hz |
3.4.5.1 All new generating units shall be capable of operation
in 47.5 to 51.0 Hz frequency range for short duration without damage or
reduction of life.
3.4.6 Reliability
Criteria
System reliability of
the GRID includes three aspects:
·
system adequacy
·
system security.
·
service
reliability
3.4.6.1 Generation Adequacy
Adequacy
is the ability of the electric system to supply the aggregate electrical demand
and energy requirements of their customers at all times, taking into account scheduled and reasonably
expected unscheduled outages of system elements.
Adequacy of the generating system is usually measured in terms of loss of load probability (LOLP) which is the probability of system capacity not being able to meet system load. LOLP can also be expressed as loss of load expectation (LOLE) in days per year. This measure does not consider the amount or duration of the capacity shortfall.
System Adequacy Limits:
Preliminary Stage: 20%
Transition Stage: 8%
Final Stage: 1% (87.6 hr/year)
3.4.6.2 Security
Security
is the ability of the electric system to withstand sudden disturbances such as
electric short circuits or unanticipated loss of system elements.
The
bulk electric system shall be designed for a security level of n-1, i.e.to
withstand a single contingency with little negative effect. This means the most
severe fault or the tripping of a critical generator, transformer or line
should not result in
a)
instability of the system
b)
overloading lines and/or transformers for more than 15
minutes
c)
voltage drop of more than 10 % when the system import is
increased by 20%
d)
load shedding
System
Security Limits:
Security
level of “n-1” (single contingency) PLUS
spinning
reserve margin of:
Preliminary
Stage: no mandatory
requirement
Transition
Stage: 0.5 % of
system peak load
Final
Stage: 1 %
of system peak load
3.4.6.3 Service
Reliability
The points where electric power is supplied from the transmission system to the Users (distribution companies, another transmission system, EHT customers) are called delivery points or grid supply points. Outages at these points directly affect the Users of the GRID. The reliability level at the delivery points is therefore an indication of the quality of service provided by APTRANSCO to its Users.
Service
reliability of the GRID is indicated by :
System
Average Interruption Frequency Index (SAIFI)
System Average Interruption duration Index (SAIDI)
which
are calculated as follows:
For
each forced outage involving one or more delivery points and lasting more than
1 minute, the following parameters are recorded:
Ø Duration of outage in
minutes: Ti (min)
Ø Sum of interrupted loads
at all affected delivery points: S Pi (kVA)
SAIFI
= SPi / Ptotal
SAIDI=
S(Pi x Ti)/Ptotal ¸ 60
Where
Ptotal = total sum of installed load at all delivery points
Note: Scheduled outages which are communicated
to the consumers beforehand and load shedding due to capacity shortage are not
counted in the computation of these indices
Allowable Limits
|
|
SAIFI |
SAIDI |
|
Preliminary Stage |
no limit |
no limit |
|
Transition Stage |
24/yr |
10 hours/year |
|
Final Stage |
18/yr |
8 hours / year |
3.4.7 Harmonic
Distortion
3.4.7.1 General
Description
Many types of equipment and phenomena can produce voltages and currents at frequencies that are multiples of the power frequency. These high frequency components are called harmonics and their ratio to the fundamental frequency is the harmonic order. Harmonics have many negative effects on the system and connected loads, so they have to be limited to a manageable level.
Control of harmonics on
the APTRANSCO system is based on
voltage harmonic distortion. Users
produce harmonics by drawing from and injecting into the system harmonic
currents which propagate through the system creating harmonic voltage drops,
thus affecting others, so control of User harmonics is based on harmonic
distortion current.
Harmonics are grouped into three categories: odd triplens (multiples of three), other odd harmonics, and even harmonics, with different severity levels and effects on equipment for each category. Odd harmonics are much more common than even harmonics.
3.4.7.2 Indicator
of Quality for System Harmonics
Harmonic contents of the supply voltage is indicated by the following
indices:
VTHD = 
VIHD =
Where Vi : ith harmonic of voltage
V1 : fundamental frequency (50 Hz) voltage
VTHD: voltage total harmonic distortion
VIHD : voltage distortion of ith harmonic
3.4.7.3 Maximum Limits of Voltage Harmonic Distortion
in HT and EHT
Systems.
Table
|
Harmonic
Order |
Distortion
% |
|
|
|
HT |
EHT |
|
(odd,
non-triplen) 5 7 11 13 17 19 23 25 >25 |
6.0 5.0 3.5 3.0 2.0 1.5 1.5 1.5 0.2+1.3x25/n |
2.0 2.0 1.5 1.5 1.0 1.0 1.0 0.7 0
.1+0.6x25/n |
|
(odd, triplen) 3 9 15 21 >21 |
5.0 1.5 0.3 0.3 0.2 |
2.0 1.0 0.3 0.2 0.2 |
|
(even) 2 4 6 8 10 12 >12 |
2.0 1.0 0.5 0.5 0.5 0.2 0.2 |
2.0 2.0 0.5 0.4 0.4 0.2 0.2 |
|
Total Harmonic
Distortion |
8% |
3% |
3.4.7.4 Control and Measurement
(a) Control
APTRANSCO shall monitor the voltage harmonic levels at the supply points to the Users (DISCOMs, AP Genco, major users) and other strategic locations on the transmission system.
APTRANSCO will compile a list of all metering points and take
measurements at 5 sites per month. The
list has to be submitted to APERC for approval.
(b) Measurement
The measurements should conform to IEC Std 1000-4-7 or IEEE Std 519. The measurements should be taken at 10 minute intervals and should last for 1 week per site.
3.4.7.5
Enforcement of Limits
The harmonic voltage
limits will be implemented in stages as follows
Preliminary
Stage
Limits not in effect
Transition Stage
APTRANSCO will monitor voltage
harmonic distortions at all delivery points, but no sanctions will apply for
exceeding the limits
Final Stage
The
limits in Section 3.4.7.3 will apply
Limits of Supply Voltage Harmonics in LT System will be included in future Versions.
3.4.8 Voltage
Flicker
3.4.8.1 General
Description
If the voltage fluctuates, the luminous intensity of
the lamps and TV’s will fluctuate correspondingly. If the fluctuation is of a magnitude and
frequency perceptible to the eye, it becomes flicker. Flicker could range from annoying to complete
interference of normal activity.
Flicker is not usually produced by the power system
but by customer loads such as arc furnaces, compressors, starting of large
motors, etc. Since voltage fluctuation
of the system affects other users on the same system, the transmission company
needs to control the flicker on its lines and station busses. At the same time, flicker-generating loads
connected to the system have to be controlled.
3.4.8.2 Indicator
of Quality for System Flicker
Flicker is measured by means of two indices, Pst and Plt, as defined in IEC Std 1000-3-7. For the purpose of regulation, Pst, the short term flicker severity index, is selected as the indicator of quality.
3.4.8.3 Limits
Pst = 1,
which is equivalent to the threshold of perception, is the allowable level of
flicker on the transmission system.
3.4.8.4
Control and Measurement
Substations which supply heavy industrial loads such as furnaces, steel mills, etc. are targets for flicker monitoring. Other substations and connection points will be selected for monitoring on a random basis. At least one site is monitored each month.
The list of monitoring points is submitted to APERC
for approval at least 2 months before the monitoring. The flicker measurement will be conducted at
10 minute intervals according to procedures outlined in IEC Std 61000-4-15.
Each site is measured for 1 week
3.4.8.5
Enforcement of Limits
Flicker limits and control and measurement procedure will be in effect only in the Final Stage
3.5 Connected Plant
Restrictions
3.5.1 General
Principle
Users connected to the Grid can produce power
disturbances which propagate to the power system. If these disturbances are severe, the power
system and other Users on the system will be adversely affected. To ensure system integrity and fairness to
all Users restrictions and controls have to be placed on Users of the system.
3.5.2 Safety
The term "Safety" refers to safety standards
adopted in manufacture, erection stages in choice of location and in
installation, operation and maintenance procedures. The term applies both to
safety to equipment and safety to persons including safety of general public
(in addition to safety of utility staff).
The equipment of the Users, including machines,
devices, overhead lines, underground cables, transformers, etc., must conform
to Safety Standards (ISS, general engineering safety standards and the safety
Codes to be issued by APTRANSCO). The
Standards of the Safety Codes to be issued by APTRANSCO shall not be lower than, or inferior to, the APSEB
Safety Manual.
3.5.3 Insulation
The Users' system must be designed with the proper
basic insulation level (BIL). Insulation of all components in service must have
adequate dielectric strength for the system operating voltages at all
times.
3.5.4. Clearances
All overhead lines, equipment and facilities of the User’s system connected to the GRID must comply with clearance limits published in the Indian Electricity Rules. For situations not covered in the Indian Electricity Rules, the IEEE C2-1997 “National Electrical Safety Code” will apply.
3.5.5 Earthing
All components of the Users' systems must be properly
earthed as per standards. All individual
earth electrodes, earthing pits, and the interconnection arrangements shall be
as per standards and shall be properly maintained.
The bodies/cases/trucks/enclosures of all items of equipment shall be properly earthed, with the actual earthing arrangements depending on the machine ratings. Metallic supports of overhead lines and cable sheaths and shields shall also be earthed as appropriate.
3.5.6 Safety Training
Personnel of all entities shall be adequately trained
in the correct operating techniques and safety precautions, keeping in mind
cross-boundary connections.
3.5.7 Motor Starting
The Motor Starting Current of motors in the Users'
systems shall be less than 6 times the full-load current unless special
exemption is granted. The appropriate
methods of motor starting shall be adopted.
Two or more motors shall not be started simultaneously or within 5
minutes if the resulting voltage dip at the substation bus exceeds 5 %.
Where necessary, APTRANSCO shall have the right to advise the consumer or User
to change over to "auto-transformer" motor starting if the existing
starting method causes unacceptable system distortions.
3.5.8 Access
to APTRANSCO
APTRANSCO and its
authorized personnel shall have the right to inspect the plant of any USER or
Consumer, to ensure conformity to standards and restrictions.
3.5.9 Unintended
and Unscheduled back-energization
The Users shall take adequate precautions to ensure
that no part of the grid is energized by the Users' system from another source
of supply unless it is requisitioned in writing by the utility as an
exceptional arrangement. The switch-gear
and controls of the Users' systems shall be so designed as to prevent
back-energisation and the personnel shall be made aware of the need for this
precaution.
3.5.10 Harmonics (Harmonic
Current Generated by Consumers)
3.5.10.1 Indicators
The level of harmonics generated by Users or customers is indicated by the percentage of harmonic distortion measured at the point of connection. The following indices are the total current harmonic distortion and the individual current harmonic distortion respectively.
ITHD = 
IIHD = 
where:
ITHD
= Total harmonic distortion of current
IIHD
= Individual distortion of current of harmonic order i
Ii = Current component of harmonic order “i”; I1 = Current component of fundamental frequency 50 (HZ)
3.5.10.2 Limits
Limits of Harmonic Current Distortion (%)
|
Harmonic
Order (n) |
P
> 10 kW or V<
33 kV |
P>50
kW or V>33
kV |
|
Odd,
Non triplen |
||
|
5 |
12 |
6 |
|
7 |
8.5 |
5.1 |
|
11 |
4.3 |
2.2 |
|
13 |
3 |
2.2 |
|
17 |
2.7 |
1.8 |
|
19 |
1.9 |
1.7 |
|
23 |
1.6 |
1.1 |
|
25 |
1.6 |
1.1 |
|
>25 |
0.8+0.8*25/n |
0.4 |
|
Triplen |
||
|
3 |
16.6 |
7.5 |
|
9 |
2.2 |
2.2 |
|
15 |
0.6 |
0.8 |
|
21 |
0.4 |
0.4 |
|
>
21 |
0.3 |
0.4 |
|
Even |
||
|
2 |
10.0 |
10 |
|
4 |
2.5 |
3.8 |
|
6 |
1.0 |
1.5 |
|
8 |
0.8 |
0.5 |
|
10 |
0.8 |
0.5 |
|
12 |
0.4 |
0.5 |
|
>12 |
0.3 |
0.5 |
|
Total |
20.0
% |
12
% |
3.5.10.3 Control
and Measurement
Measurements may be taken at any time by APTRANSCO at the
customer’s connection point.
Measurements have to be taken in accordance with methodologies of IEC
61000-4-7 or IEEE STD 519-1992 and have to be for at least 24 hours long at 10
minute measurement intervals.
3.5.10.4 Enforcement of Limits
The customer load harmonic limits will be implemented in stages as follows:
Preliminary Stage
Limits
not in effect
Transition Stage
APTRANSCO
will monitor current harmonic distortions at all delivery points, but no
sanctions will apply for exceeding the limits
Final Stage
The
limits in Section 3.4.10.2 will apply
Limits of Current Harmonics in LT System will be included in future versions of CTI.
3.5.11 Voltage
Flicker Generated by Users
3.5.11.1 General Description
Some customer loads draw intermittent current (e.g.
arc furnace) or create a steep increase in current (e.g. motor start). If this happens frequently and if the
magnitude of current is significant, the resulting voltage fluctuation will be
sufficient to cause flicker. As an
obligation to other customers, the flicker produced by customers has to be
restricted.
3.5.11.2 Indicator
Flicker
generated by customers is indicated by the index Pst as defined in IEC Standard
61000-3-7 and measured with a flicker meter that meets the specification of IEC
Std 868 or IEC Std 61000-4-15
3.5.11.3 Limits
Tolerance for customer-generated flicker varies with the relative strength (short circuit ratio) of the load and voltage level. Limits are given in the following table.
Limits of
flicker produced by Users
|
Short Circuit Ratio SL/SCC |
Voltage |
Pst |
|
SL/SCC
£ 0.04 |
HT |
0.37 |
|
EHT |
0.58 |
|
SL/SCC
> 0.04 |
HT |
0.8 |
|
EHT |
1.0 |
3.5.11.4 Control and Measurement
Flicker is measured at the point of connection using
an approved flicker meter and in accordance with IEC Std. Measurement must be taken for at least 24
hours at 10 minute measurement intervals.
Flicker readings with the load off must be taken for at least 5 hours as
a reference.
3.5.11.5 Enforcement of Limits
Flicker limits and control and measurement procedure will be in effect only in the Final Stage
3.5.12 Power
Factor
3.5.12.1 General description
It is desirable that loads on the system have power factors at or close to unity as that represents the most efficient use of the system capability and the least loss of energy. It also eliminates many transient stability problems. Any load with a power factor lower than 90% is imposing an unfair burden on the transmission system and other Users. Power Companies therefore place restrictions on the power factors of customer loads.
3.5.12.2 Limit
The
minimum power factor allowed is 90%.
3.5.12.2 Control and Measurement
Power factor measurements are made continuously in
conjunction with the voltage measurements. Loads with inherent low power
factors should automatically include capacitors to correct the problem.
3.5.12.3 Penalty
A user with power factor worse than 90% may be refused connection to the transmission grid until the problem
is rectified. Alternatively, a penalty may be assessed.
3.5.12.4 Enforcement of Limits
The
limit for power factor shall be effective immediately.
3.5.12.5 Reactive
Power Requirements: In general the Distribution Companies shall not depend on APTRANSCO and APTRANSCO shall not
depend on ISTS for reactive support.
DISCOMS shall provide reactive compensation for their systems and
APTRANSCO shall provide reactive compensation for the
intra state Transmission system.
The DISCOMs shall ensure that consumers having inductive load install
capacitors. The DISCOMs shall also install capacitors at various locations of
the Distribution System so that at the interface with APTRANSCO the power
factor is not less than 90%.
3.6 Operational Numbering and
Nomenclature Standards
3.6.1 Introduction
Numbering and nomenclature of plant and apparatus at connection sites specifies responsibilities and procedures for determining and notifying APTRANSCO and Users of the other’s plant and apparatus at connection sites. Nomenclature shall include the selections of sub station names.
The numbering and nomenclature of plant and apparatus shall be included in the ownership diagram prepared for each connection site.
3.6.2
Objective
3.6.3 Procedure for numbering and nomenclature of plant and
apparatus at connection sites.
3.6.3.1 Plant and apparatus of new connection sites
When APTRANSCO or a User intends to install an apparatus at a new connection site, the proposed numbering and nomenclature shall be notified as part of the production of the ownership diagram or operation diagram in accordance with the provisions of the connection conditions. The principles to apply will be those set out in this Section.
3.6.3.2 Existing connection sites
a) When APTRANSCO or a User intends to install plant and
/ or apparatus at an existing connection site the proposed numbering and / or
nomenclature to be adopted shall be notified to the other.
b) The notification shall be in writing and will consist of a revised ownership diagram incorporating the proposed plant and numbering and nomenclature.
c) The notification shall be made at least six months prior to the proposed installation or such shorter period as APTRANSCO or the User may agree.
d) The Recipient of the notification shall respond in writing within one month confirming receipt and whether the proposed numbering and/or nomenclature is acceptable. If unacceptable the response shall state what would be acceptable.
e) In the event that agreement cannot be reached between
APTRANSCO and the User, APTRANSCO acting reasonably shall have the right to
determine the numbering and nomenclature to be applied.
3.6.3.3 Changes
to Existing plant and apparatus.
Where APTRANSCO or a user needs to change the existing
numbering or nomenclature of any of its plant and / or apparatus at a
connection site, the provisions of 3.5.3.2 shall apply with amendments
necessary to reflect that only a change is being made.
Clear Labelling:
APTRANSCO and each user shall be
responsible for the provision, execution and maintenance of clear and
unambiguous signs/labels showing the numbering and nomenclature of its plant or
apparatus of connection sites
3.7 Protection Requirements & Co Ordination
3.7.1 General
Principles
No item
of electrical equipment shall be allowed to remain connected to the
Transmission System unless it is covered by appropriate protection aimed at
reliability, selectivity, speed, discrimination and sensitivity. Guidelines mentioned in protection manuals of
CBI & P shall be kept in view.
Protection standards are treated as interface issues
because of the possible severe cross-boundary repercussions of faults that
occur in the system of any entity.
Minimum protection requirements are prescribed in the Section because inadequate protection or
mal-operation of protection system of one entity may result in far reaching
consequences, disturbances and even damages in the systems of other
entities.
All Users shall co-operate to ensure correct and
appropriate settings of protection to achieve effective, discriminatory removal
of faulted equipment within the target clearance times specified in this
Section.
The protection systems to be installed (or kept in
service) at various Generating Stations and sub-stations shall not be inferior
to the systems existing before the effective date under the erstwhile Andhra Pradesh State
Electricity Board. The Corporations
shall update the protection system as technology advances worldwide. The
protection standards existing in AP State just before restructuring are given
in 3.6.3.1 to 3.6.3.4. the features and
functions of the various relays should have minimum protective capability
obtaining before re-structuring.
Protection settings shall not be altered without
consulting and informing all affected Users. No protection should be by-passed
or disconnected without the agreement of the affected User. When protection is
bypassed and/or disconnected by agreement, then the cause must be rectified and
the protection restored to normal condition as quickly as possible. If
agreement has not been reached the electrical equipment shall be removed from
service forthwith. Even when protection
is temporarily bypassed by agreement, a standby protection or back-up
protection system shall be operational during the period.
The APTRANSCO
shall be responsible for arranging periodical meetings among all Users to
discuss coordination of protection. APTRANSCO shall investigate any
maloperation, non-operation or delayed operation of protection or other
unsatisfactory protection performances. Users shall take prompt action to
correct any protection malfunction or issue as discussed and agreed to in these
periodical meetings. APTRANSCO shall
determine the relay settings of all Transmission lines and communicate to Generating stations and DISCOMs. APTRANSCO shall determine relay settings at all EHT Sub-Stations
upto the
3.7.2 Fault
Clearance Times
The maximum fault clearance
times for faults based on stability consideration on any User's system directly
connected to the Transmission System, or any faults on the Transmission System
itself, are as follows.
Target Clearance Times
|
Voltage Class |
Total Relay Operation Time + Breaker
Opening Time |
|
400 Kv |
100 msec |
|
220 kV |
160 msec |
|
132 kV |
160 msec |
The above times shall apply after
carrier inter trip and auto reclosure features are commissioned in the
APTRANSCO System.
Slower fault clearance times for faults on a Users
system may be agreed to if, in the
opinion of APTRANSCO, the system
conditions will allow. APTRANSCO shall specify the required
opening times of circuit breakers at various locations owned by Generators and DISCOMs.
3.7.3 Protection
Requirements
3.7.3.1 Generator Requirements
All Generating Units and associated electrical equipment of the Generating Units connected to the Transmission System shall be protected by adequate protection so that the Transmission System does not suffer due to any disturbance originating from any Generating Unit. The protection schemes shall be in accordance with the CBIP guide lines which are indicated below:
The following are the minimum protection requirements of Alternators and Generator Transformers at Generating Stations: -
(i) Generator Differential
(ii) Overall Differential
(iii) Minimum Impedance (alternatively over current/under voltage)
(iv) Negative Sequence
(v) Stator Overload
(vi) 95% Stator Earth Fault
(vii) 100% Stator Earth Fault
(viii) Loss of Excitation
(ix) Pole Slip
(x) Low Forward Power/Reverse Power (double protection for large alternators).
(xi) Minimum Frequency
(xii) Over Voltage or Over Current (protection against inter-turn faults)
(xiii) Over-fluxing (voltage/Hz)
(xiv) Over Voltage
(xv) Protection against accidential Energisation of Dead Machine
(xvi) PT Fuse Failure
(xvii) Rotor Earth Fault
Generator Transformers
(i) Overall Differential
(ii) Over Current
(iii) Earth Fault
(iv) Restricted Earth Fault
(v) HV winding-cum-overhang differential
(vi) Buchholtz Protection
(vii) Local Breaker backup protection
Unit Auxiliary
Transformer
(i) Transformer Differential
(ii) Over Current
(iii) Residual Over Current
(iv) Restricted Earth Fault
(v) Buchholtz Relay
(Note: Exemption may be given to small generating units for some of the protections.)
In this sub-section only those protections which have direct impact on the Grid are prescribed. Other protections of the Alternator and Transformers and the various protections for the Turbine, Boiler and Auxiliary Machines are considered the internal issues of the Generators and hence not dealt here.
3.7.3.2 Transmission
Requirements
General: Every EHT line taking off from a Power Station or a
Sub-Station shall have distance protection and back up protection as mentioned
below. The APTRANSCO shall notify Users of any changes in its policy on
protection from time to time. All 400 kV
lines and 220 kV lines owned by APTRANSCO
shall have two fast operating distance protection schemes preferably with two
different operating principles the voltage
of one relay being fed from Bus P.T. and the voltage of the other relay
from line CVT, the currents of the two relays being fed from different CT
cores. There shall be facility to change
over voltage supply to relays from Bus P.T to C.V.T. and vice versa. Additional
back up protection may be provided by APTRANSCO
at its discretion.
400 kV
Lines: Three zone static fast
acting distance protection with
permissive inter trip for accelerating tripping at remote end in case of zone-2
fault as Main 1 protection. Main 2
protection shall be similar fast acting protection using direction comparison
or phase comparison carrier relaying scheme. Main 1 and
In addition to the above single pole tripping and
single shot single pole auto reclosing after an adjustable dead time shall be
provided.
Main 1 and
220 kV lines:
Necessary indications, alarms and controls shall be
provided for P.T. supply failure and for ensuring change over from Bus No.1 PT
to Bus No.2 PT and vice versa when Bus
Transfer is made.
Presently carrier inter trip has not been installed by APTRANSCO. This feature shall be provided in due course
for accelerating tripping at the remote end in case of faults covered by Zone 2 from one end.
132 kV
Lines: Three zone static or electromagnetic distance
protection as main protection. Carrier inter-trip feature shall be provided as
soon as possible. The back up shall be
directional IDMT over current relays and one directional IDMT earth fault
relay.
For short transmission lines alternative protection
schemes may be adopted.
The tripping and relay indications in respect of
Feeders supplied from the switchyard of a generating station shall be promptly
informed by the operator at the Generating Station to the operating engineer of
APTRANSCO and to SLDC.
The following shall be taken as approved protection norms for Transmission and Distribution lines.
NORMS OF PROTECTION FOLLOWED DURING ERSTWHILE APSEB
REGIME.
FOR TRANSMISSION & DISTRIBUTION LINES: -
|
S.No
|
Voltage
|
Protection Scheme
|
|||
|
1.
|
220 K V Line
|
|
|||
2
|
132 K V Line
|
Main
Protection:- Switched distance scheme (fed from bus PT)
Backup Protection:- 3 Nos directional IDMT O/C Relays and 1 No directional IDMT E/L relay. |
|
|||
3
|
33 K V Lines
|
Non-directional IDMT 3 O/C and 1 E/L relays. |
|
|||
4
|
11 K V Lines
|
Non-directional IDMT 2 O/C and 1 E/L
relay.
|
|
|||
Notes:
(i) On some of the old 220 kV lines one distance scheme with backup directional IDMT 3 O/L & 1 E/L relays were provided.
(ii) On some of the 132 kV grid lines, only distance scheme is available.
(iii) Very few 66 kV lines are in service (which are also being phased out) with distance OC/EL relays.
3.7.3.2.1 Earthing: The transmission system design and the selection of vector group of EHT Transformers shall be such that the Earth Fault Factor is below 1.4
3.7.3.3
Distribution Line Requirements
All 33 kV and 11 kV lines shall be provided with a minimum of over current and earth fault protection with or without directional features as given below.
Plain Radial Feeders:
Three Non-directional
time-lag overcurrent relays one non-directional IDMT Earth Fault Relay with
suitable settings to obtain discrimination between adjacent relay stations.
Parallel
Feeders/Ring Feeders:
Directional
time-lag overcurrent and earth fault relays.
Long
Feeders/Transformer Feeders:
For long feeders or transformer feeders, the relays
should incorporate a high set instantaneous element within five years from the
effective date..
The relay settings of the Distribution systems shall be determined by the DISCOMS in agreement with APTRANSCO.
3.7.3.4 Transformer Requirements
Generating
Station / Transmission System: All
windings of autotransformers and power transformers of EHT class shall be
protected by differential relays. Overfluxing relays shall be provided for HV
and LV of EHT transformers. In addition there shall be back up time lag over
current and earth fault protection. For
parallel operation such back up protection shall have a directional
feature. For protection against heavy
short circuits, the over current relays should incorporate a high set
instantaneous element. In addition to
electrical protection, gas operated relays, winding temperature protection and
oil temperature protection shall be provided.
Distribution System: Up to (but Excluding )15 MVA, Non-directional IDMT overcurrent relays (3 nos) and earth fault relay (1 No) both on HV and LV side Instantaneous REF shall be provided within 5 years from the effective date.
For smaller transformers of 66 kV/33kV/11kV class on
the Distribution System, differential protection shall be provided for 15 MVA
and above along with back up time lag over current and earth fault protection
(with directional feature for parallel operations).
All Power Transformers, 1.6 MVA and above, shall be
provided with Buchholtz relay, winding temp and Oil temp. protection in addition to the above mentioned
relays. For 1.6 MVA and 3.0 MVA
Transformers circuit breakers do not exist on HV side hence the protections serve to isolate load
and initiate alarms.
The following shall be approved norms of protection for transformers of different voltage classes and capacity ratings:-
NORMS OF PROTECTION FOR EHV CLASS POWER TRANSFORMERS
(existing in erstwhile APSEB Regime.)
|
Voltage ratio & capacity |
H V Side |
L V Side |
Common relays |
|
i) 132/33/11
K V upto
8 M V A |
3 O/L relays + 1 E/L relay |
2 O/L relays +
1 E/L relay |
Bucholz, OLTC Buchlolz,
OT,WT |
|
ii) 132/33/11 K V above
8 MVA and
below 31.5 MVA. |
3 O/L relays + 1 dir. E/L relay |
3 O/L relays + 1 E/L relay |
Differential, , Bucholz, OLTC Bucholz, OT, WT. |
|
iii) 132/33 K V 31.5.
MVA and above |
3 O/L relays + 1 dir. E/L relay |
3 O/L relays + 1 E/L relay |
Differential, Overflux, Bucholz, OLTC Bucholz, PRV, OT, WT. |
|
iv) 220/33/ KV 31.5
MVA & 50
MVA 220/132
KV 100
MVA |
3 O/L relays + 1 dir. E/L relay |
3 O/L relays + 1 dir.E/L relay |
Differential, Overflux, Bucholz, OLTC Bucholz ,PRV, OT, WT |
|
v) 400/220 KV 315
MVA |
3 directional O/L relays (with dir. Highset) + 1 directional E/L relay. Restricted E/F relay |
3 directional O/L relays (with dir. highset) + 1 directional E/L relay. Restricted E/F relay |
Differential, Overflux, Bucholz, OLTC Bucholz PRV, OT WT and overload (alarm) relay. |
3.7.3.5 Substation Bus Bar Protection
Adequate bus zone protection for substation bus bars in all 400 kV and 220 kV class substations shall be provided.
LBB: At all 400 kV & 220 kV
substations Local Breaker Back up protection shall be provided.
3.7.3.6 Fire Protection
Fire protection systems and regulations shall be in
accordance with relevant Indian Standard Specification and provisions in IE
Rules & Tariff Advisory Committee (TAC). Where appropriate Indian rules do
not exist or are not applicable, NFPA Fire Protection Manual or IEC standards
(or better standards) shall apply
3.7.3.7 Data Requirements
a) Full description including settings for all relays and protection systems installed on the Generating Unit, Generating Unit Transformer, Auxiliary Transformer and electrical motors of major equipment listed.
b) Full description including settings for all relays installed on all outgoing feeders from power station switchyards, tie circuit breakers, incoming circuit breakers.
c) Full description of inter-tripping of circuit breakers at the point or points of connection with the APTRANSCO system.
d) Most probable fault clearance times for electrical faults on the User's system.
e) Relay protection installed for all transformers and feeders along with their settings and level of co-ordination with other Users.
f) See Section 2 (Planning Code) Appendix C for a summary of the protection data requirements.
g) Data required for determination of short-circuit current at each point of connection and rupturing capacities of breakers shall be exchanged between utilities.
h) Data as prescribed in the Annexures to Planning Code in various contexts.
3.8 Earthing
Where a point in EHT system of APTRANSCO is earthed
the Earth Fault Factor shall be below 1.4
(Like most stipulations in the Connection Code the
clauses in the following paras must be taken into account by the Generators
while placing orders of equipment on Manufacturers)
3.9 Design Parameters of New
Generating Units.
(i) New Units: For new plant para 3.2.5
(a), this para (3.9) and other paras of this Code apply. For plant existing as
on the Transfer date the actual specifications hold for the life period of the
equipment. However if certain parts can be replaced at reasonable investment
then those parts shall be replaced under a Renovation, Rehabilitation and
Modernization Programme to ensure better performance to conform to the
requirements of CTI and IEGC. For example the Generators shall replace the
Turbine Speed Governors and AVR systems of the alternators, and instal Power
System Stabilisers if technically possible in order to meet the operating
standards of the CTI and IEGC.
In addition APTRANSCO may require Generators to comply
with other specifications in a bilateral agreement before the Connection
Application is accepted in order to ensure the required performance of the
transmission system and the total system.
(ii)
The Generating
Units shall be capable of supplying rated active power output between 0.85
power factor lagging and 0.95 power factor leading.
(iii)
The Short Circuit
Ratio of Generating Units shall be not less than 0.5.
(iv)
A Generating Unit
shall be capable of supplying rated active power output within the system
frequency range 49.5 to 50.5 Hz.
(v)
Decrease of output with decrease of frequency: Any decrease of output in the frequency range 49.5 to
47 Hz should not be more than pro rata with frequency. The Generating Units
must be capable of operation in 47.5 to
52 Hz range for a short duration without any deleterious effects and without
reduction of life.
(vi)
Effect of Voltage Fluctuations: The MW
output of a Generating Unit should not be affected by voltage changes in the
permissible range. The Reactive Power Output under steady state conditions
should be fully available as per capability curves within a voltage range of ±
5% of nominal value.
(vii)
Governors: All new Generating units must have automatic Governors
with a droop of 3 to 6% and automatic voltage regulators. Power System
Stabilizers shall be installed under a bilateral agreement with APTRANSCO. All new units shall have provision for
incorporating power system stabilizers, if not provided at the time of initial
commissioning.
(viii)
Overloads:
All new Generating units must be capable of instantaneously increasing the
output (by auto governing action) by 5%
for a minimum of 5 minutes (upto 105% MCR) when the system frequency falls.
(ix)
The HV winding of
the Generator Transformer must be star connected with the star point suitable
for earthing. The earthing of HV star point and the configuration of
(x)
CCGT Modules
meant for Central Despatch must have Fast-Start capability so that SLDC may use
them for Operating Reserve.
(xi)
Thermal Units
must be capable of continuous stable operation at any load between 60% MCR and
100% MCR without oil support and between 45% and 60% MCR with oil support.
(xii)
Hydel Units must
be capable of continuous stable operation at any load between 40% MCR and 100%
MCR.
Whenever APTRANSCO
implements