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State of Madhya Pradesh - Section

Section 15 in Madhya Pradesh Electricity Grid Code (Revision-II), 2019

15. Section 15

Protection
15.1Introduction
15.1.1In order to safeguard State Transmission System, Users' system from faults it is essential that certain minimum standards for protection be adopted. This section describes these minimum standards.
15.1.2If any of the provision not covered under protection code of MPEGC, the same as specified under Central Electricity Authority (Grid Standards) Regulation, 2010 shall be applicable. If any of the provisions of the existing Protection Code of Madhya Pradesh Electricity Grid Code is inconsistent with any of the provisions of CEA (Grid Standards) Regulations, 2010, the provisions of Regulations made by CEA shall prevail.
15.2Objective. - The objective of this section is to define the minimum protection requirements for any equipment connected to the State Transmission System and thereby minimize disruption due to faults.
15.3General Principles
15.3.1Protection standards are treated as interface issues because of the possible severe inter- user boundary repercussions of faults that occur in the system of any entity. Minimum protection requirements are prescribed in this section because inadequate protection or mal-operation of protection system of any entity may result in far reaching consequences, disturbances and even damages in the systems of other entities.
15.3.2No item of electrical equipment shall be allowed to remain connected to the State Transmission System unless it is covered by minimum specified protection aimed at reliability, selectivity, speed and sensitivity.
15.3.3All Users shall co-operate to ensure correct and appropriate settings of protection to achieve effective, discriminatory removal of faulty equipment within the time for target clearance specified in this section.
15.3.4Protection settings shall not be altered, or protection bypassed and/or disconnected without consultation and agreement of all affected Users. In the case where 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 will be removed from service forthwith.
15.3.5For the following, STU will also be guided by the advise of WRLDC:
(i)Planning for upgrading and strengthening protection system based on analysis of grid disturbance and partial/total blackout in State Transmission System.
(ii)Planning of Is-landing and system split schemes and installation of Under Frequency Relays and df/dt relays.
(iii)Under-Frequency relay for load shedding, Relays provided for is-landing scheme, disturbance recorder and fault locater installed at various substations shall be tested and calibrated. The Protection Practices and Protocol Manual shall have provision for the same.
15.4Protection Co-ordination. - A Protection Coordination Committee (PCC) shall be constituted as per Section 3 of the Grid Code and shall be responsible for all the protection coordination functions defined under the same section. STU shall be responsible for arranging periodical meetings of the Protection Coordination Committee. STU shall investigate any malfunction of protection or other unsatisfactory protection issues. Users shall take prompt action to correct any protection mal-function or issue as discussed and agreed to in the periodical meetings
15.5Fault Clearance Times & Short-time Ratings. - From a stability consideration, the minimum short circuit current rating and time and the maximum fault clearance times for faults on any User's system directly connected to the State Transmission System, or any faults on the State Transmission System itself, are as follows:
Nominal Voltage Minimum Short Circuit current rating Target Fault clearance Time
kV kA (rms) Seconds msec.
765kV     100
400kV 40 1 100
220kV 31/40 1 160
132kV 25/31 3 160
Slower fault clearance times for faults on a users system is not allowed from system security point of view. STU shall specify the required opening time and rupturing capacity of the circuit breakers at various locations for STU and Discoms/Open access users directly connected to Transmission System. At generating stations, line faults should be cleared at the generation station end, within the critical clearing time, for the generators to remain in synchronism.
15.6Generator Requirements
15.6.1The guidelines mentioned in the "Manual on protection of Generators, Generator Transformers, and 220 kV and 400 kV networks" vide publication no 274 of CBIP shall be kept in view.
15.6.2All Generating Units and all associated electrical equipment of the Generating Units connected to the State Transmission System shall be protected by adequate protection so that the State Transmission System does not suffer due to any disturbances originating from the Generation unit. The generator protection schemes shall cover at least Differential protection, back up protection, Stator Earth fault protection, field ground/field failure protection (not applicable to brush-less excitation system), negative sequence protection, under frequency, over flux protection, backup impedance protection and pole slipping protection (applicable to units above 200MW), loss of field protection, reverse power protection etc.
15.7Transmission Line Requirements
15.7.1General. - Every EHV line taking off from a Power Station or a sub-station shall have protection and back up protection as mentioned below. STU shall notify Users of any changes in its policy on protection from time to time.
For short transmission lines, alternative appropriate protection schemes may be adopted. Relay Panels for the protection of lines of STU taking off from a Power Station, shall be owned and maintained by Generator. Any transmission line related relay settings or any change in relay settings will be carried out by the Generator in close co-ordination and consultation and with STU approval. All such issues shall be put up in the next Protection Coordination Committee for ratification. Carrier cabinets/equipment, Line matching units including wave traps and communication cable shall be owned and maintained by STU. All Generators shall provide space, Connection facility, and access to STU for such purpose.
15.7.2400kV Transmission Lines. - All 400kV transmission lines owned by STU shall have two fast acting protection schemes, the voltage of the two relays shall be fed from two different cores of the line CVT and the currents of the two relays shall be fed from two different cores of the line CTs.
Main 1. - protection scheme shall be numerical, three zone, non-switched fast acting distance protection scheme with permissible inter-trip at remote end (in case of zone-2 fault)Main 2. - protection scheme shall be either similar type of numerical, three zone, non-switched fast acting distance protection scheme with permissible inter-trip at remote end (in case of zone-2 fault) OR a unit protection scheme employing transient wave detection, directional comparison or phase comparison carrier relaying scheme.One pole tripping and single shot auto-re-closing with adjustable dead-time shall be provided.
15.7.3400kV Bus-bars. - All 400KV Substations for 400KV of bus shall have numerical bus bar differential protection scheme along-with LBB and auto re-closures for transmission lines.
15.7.4220kV Transmission Lines. - AU 220kV transmission lines owned by STU shall have single, numerical, three zone, non-switched fast acting distance protection scheme, preferably with permissible inter- trip feature at remote end (in case of zone-2 fault), single pole tripping and single-shot single pole auto-re-closing with adjustable dead-time shall be provided. For back-up protection, three directional IDMTL over current relays and one directional earth fault relay shall be provided. For short transmission lines, appropriate alternative protection schemes may be adopted.
15.7.5220kV Bus-bars. - All 220KV Sub station for 220KV Bus shall have numerical bus bar protection scheme. Also on lines connected with Generation in feed, PGCIL, single pole carrier tripping and single shot single pole auto re-closing shall be provided.
15.7.6132kV Lines. - A single three zone switched/non switched numerical distance protection scheme shall be provided as main protection. The backup protection shall be directional/non-directional IDMTL 2 over current + 1 E/F relay. For feeders connected with power stations the backup protection shall be directional IDMTL 20/C+1E/F relay
15.8Transformer Requirements
15.8.1The protection of Auto Transformers, Power Transformers and Distribution Transformers shall be as per revised manual on transformers published by Central Board of Irrigation and Power (CBIP) Publication No. 275.
15.8.2All windings of Auto Transformers and power transformer of EHT class shall be protected by differential relays having percent bias and harmonic restraint features.
15.8.3Over-fluxing relays shall be provided for EHT transformers.
15.8.4All 400kV class transformers shall have Restricted Earth Fault (REF) protection for winding.
15.8.5In addition, there shall be back up IDMTL over current and earth fault protection.
15.8.6For parallel operation, such back up protection shall have directional feature. For protection against heavy short circuits, the over current relays should incorporate a high set instantaneous element, wherever overall co-ordination permits the same. However, it should not grip due to inrush of the magnetising current and should not be set to such a high value, which is not beneficial to transformer.
15.8.7In addition to electrical protection, gas operated relays, winding temperature protection and oil temperature protection shall be provided.
15.8.8It is recommended that the following minimum protections should be provided for transformers:
(a)All 400kV class power transformers shall be provided with differential, REF, open delta (Neutral Displacement Relay) and over-fluxing relays. In addition, there shall be back up IDMTL over current and earth fault protection. For parallel operation, such back up protection shall have inter-tripping of both HT and LT breakers. For protection against heavy short circuits, the over current relays should incorporate a high set instantaneous element. In addition to electrical protection, transformer own protection viz. buchholz, OLTC oil surge, gas operated relays, winding temperature protection, oil temperature protection, PRV relay shall be provided for alarm and trip functions. It is recommended to have Double PRV protection scheme for transformer tank.
(b)All 220kV class power transformers shall have same protections as mentioned in Sections 15.8.8 (a) except REF protection.
(c)For 132kV and 33kV class transformers of capacity 5 MVA and above, the protections shall be same as mentioned in Sections 15.8.8 (a) above except over- fluxing relays, REF and PRV.
(d)For 33kV class power transformers of less then 5 MVA capacity provided on either Transmission or Distribution System, over-current with high set instantaneous element along with auxiliary relays for transformer trip and alarm functions as per transformer requirements, shall be provided.
15.9Sub-Station Fire Protection. - Adequate precautions shall be taken and protection shall be provided against fire hazards to all Apparatus of the Users conforming to relevant Indian Standard Specification and/or provisions in I.E. Rules.
15.10Calibration & Testing. - The protection scheme shall be tested at each 400kV, 220kV, 132kV, 66kV sub- station by STU once in a year or immediately after any major fault, which ever is earlier. Setting, co- ordination, testing and calibration of all protection schemes pertaining to generating units/stations shall be responsibility of MPPGCL. The overall co-ordination between MPPGCL and STU shall be decided in meeting of Protection Co-ordination Committee. The Protection Co-ordination Committee shall review the testing and calibration as and when needed.
15.11Data Requirements. - Users shall provide STU with data for this section as specified in APPENDIX 'D' of Data Registration section.