NDPL CASE STUDY - Protection Requirements for Power Distribution by R. N. Kumar GM, NDPL Nilesh N. Kane Sr. Manager, NDPL.

NDPL CASE STUDY - Protection Requirements for Power Distributionby

R. N. KumarGM , NDPL

Nilesh N. KaneSr. Manager, NDPL

CENTRAL BOARD OF IRRIGATION AND

POWER5th International Conference on Power System Protection

and Automation

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Flow of Presentation

o Overview of NDPL network

o Transformation for betterment

o Exploration in Relaying

o Exploitation of Relay facilities

o NDPL Case Studies

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Overview of NDPL Network

o NDPL is a Joint venture of TATA Power and Govt. of NCT of Delhi

o NDPL looks after Power Distribution of North and North-west area of Delhi

o Area of distribution network - 510 sq. km

o Total number of 66/33 KV Grid Stations – 59

o No. of Distribution Transformers – 9000

o Total no. of RMU’s - 8500

Transformation

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Transformation – Protection Reliability

o System reliability and availability is the main focus of a power distribution utility.

o Protection and control system and its timely and correct operation during faults is an important and crucial aspect in efficient and successful operation of Power distribution utilities.

o NDPL has completed its GSAS (Grid Substation Automation Scheme) project in 2005

o Grids were commissioned with use of IED’s that are compatible to SCADA

o This transformation from Electromechanical to Numerical relaying lead to better system reliability.

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Transformation – Grid Stations

After GSAS in Grid

Substations

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Transformation – Distribution

PRE - GSAS POST - GSAS

Old Switch Gears New Ring Main Units

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Transformation Stages

PRE- GSAS POST- GSAS

Electromechanical relays were used in all the panels.

Numerical relays were used in all the new panels commissioned after GSAS commissioning work.

No time synchronization feature is available in the relay. Electromechanical relays are prone to sluggish operation.

Time synchronization of all the Numerical relays with Data control center.

No FDR/ waveform/ event list can be downloaded and hence Fault analysis becomes a tedious job.

Availability of FDR / Waveform/Event in milliseconds resolution helps in detailed analysis of various faults.

Electromechanical relays are single function relay.

They are multifunctional IED’s i.e. Measurement/ Protection/ Control.

Limitation of feature in the relay i.e. operational only for selected protection element and no internal logic can be developed.

Inbuilt logic development feature in the relay for the purpose of better coordination.

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Expectations from newly adopted relaying system

o Redundancy of Protection functions in terms of

o Main/Backup relay.

o Multiple protection elements.

o Communication compatibility for SCADA systems.

o Fast operation of the system with correct indication

o Improvement of the system with faster Corrective and Preventive Actions.

o Efficient and Correct Fault Discrimination

o Record of Real time metering along-with its quality features

o Online Diagnosis and relay setting

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Distribution Fault Restoration using FPI’s

NO

Fault occurrenceo Upstream Breaker Openso FPI indicate fault

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Effective Distribution Protection

Application cum Coordination

Various characteristics like NI/VI/EI have been effectively used from grid to RMU to accommodate stiffer relay setting coordination of even 250ms.

Customer satisfaction has been ensured through faster restoration of supply.

Average restoration time o Grid tripping : 1.12 hrso Tripping at FSS : 38 Minuteso Av. Tripping per month : 700o Trippings reduced to 300o Downtime reduction/month : 260 hrs

Exploration

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Improvement in System Reliability

o All Protection relays cum BCU’s are well protected with Password. Separate Passwords for operation and Protection facilitate safe Protection settings and eliminated tampering of the relay settings.

o Ultimate Goal of the Automation is to operate the system in Unmanned mode. Mimic diagrams and friendly relay functions of the Relay helps breakdown team to visualize and understand the fault and operation.

o Additional Trip Supervision relay and wiring has been reduced by using status inputs of the Numerical Relay.

o Following Logics has been Configured in the relay for having effective control and Protection of the system without conventional hard wiring.

1. CBFP cum LBB Scheme.2. Reverse Blocking Scheme for Bus bar Protection.3. No requirement of the Annunciation fascia due to availability of sufficient

Configurable LED’s on relay itself.

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Scheme/Logic Implementation

Important Projects/Logics includes:

• Reverse Blocking

• Local Breaker Backup

• Transformer Monitoring Unit

• CAP ON TAP

• Remote Relay Parameterization

• Multiple Relay setting groups

• Safety concerns tackled with relaying

• Life assessment of Lightning Arrestors

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CT SATURATION AT 33 KV AIR KHAMPUR GRID

SATURATED CORES

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FAULT DATA EVENTS for AIR Khampur Created by AREVA / S&R-103

Output date 02.02.2007

Fault records file (SFD format)

Fault date 29.01.07

Fault time 13:38:30.114

synchronized Yes

Reference time for tRel(s) Recording start time

tAbs | tRel(s) | xxx.yyy Description | Value

------------------------------------------------------------------------

13:38:30.114 | 0.000 | 041.210 DIFF Enabled | Present

13:38:30.114 | 0.000 | 036.090 PSS PS 1 active | Present

13:38:30.114 | 0.000 | 034.046 LOGIC Enabled | Present

13:38:30.114 | 0.000 | 034.075 LOGIC 1 set externally | Present

13:38:30.114 | 0.000 | 034.076 LOGIC 2 set externally | Present

13:38:30.114 | 0.000 | 034.077 LOGIC 3 set externally | Present

13:38:30.114 | 0.000 | 034.078 LOGIC 4 set externally | Present

13:38:30.114 | 0.000 | 034.079 LOGIC 5 set externally | Present

13:38:30.114 | 0.000 | 034.080 LOGIC 6 set externally | Present

13:38:30.114 | 0.000 | 034.081 LOGIC 7 set externally | Present

13:38:30.114 | 0.000 | 034.082 LOGIC 8 set externally | Present

13:38:30.171 | 0.057 | 041.116 DIFF Sat.discr. 2 trigg. | Start

13:38:30.171 | 0.057 | 041.117 DIFF Sat.discr. 3 trigg. | Start

13:38:30.171 | 0.057 | 041.125 DIFF Meas.system 2 trigg. | Start

13:38:30.171 | 0.057 | 041.126 DIFF Meas.system 3 trigg. | Start

13:38:30.178 | 0.064 | 041.115 DIFF Sat.discr. 1 trigg. | Start

CASE STUDY 4 Tripping of 11 KV Incomer-

2 Tripping without indication on Outgoing

fault in 33 KV

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Observations1. It was found that at high currents with unbalance, the 11 kV Incomer-2 was tripping without indication.

2. It was found that the tripping was occurring through series trip coil mounted on the 11 kV Incomer breaker.

3. It was found that the series trip relay (CDG), though not operated gave a trip signal to the breaker when secondary injection was carried out on Phase to neutral CT.

4. On checking the wiring of the series trip relay and the tripping circuit, one wire was found broken as shown in diagram. Breaker was tripping through series trip coil which was operating on spill current due to unbalance in system.

Analysis For Wazirabad Inc. 2 tripping without indication during outgoing fault.

=> Series Trip Coil=> CDG relay Coil => CDG Relay NC contact.

C11

C31

C51

C71

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Conclusion & Corrective Action

1. As the interconnection between NC Contact and Neutral terminal was disconnected due to defective lug crimping, the unbalance current, whenever present, was not being bypassed by the NC contact of the relay. Instead, the current was going through the series trip coil, thereby making relay settings redundant. This was leading to the tripping of 11 kV Inc.2 breaker tripping on any unbalance or fault.

2. Necessary correction wiring of contacts was done and Unbalance was simulated to check the correct operation of the relay .Now Control circuit and relay functionality found OK.

CASE STUDY 5 Tripping Analysis report

for 11 KV Mithila Vihar feeder along with 11 KV

Incomer

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Critical Analysis

11 KV Incomer-1 11 KV Incomer-2

Mithila ViharNithari feeder

Both feeders running on same pole generally face external faults simultaneously

Incomer sees vector summation of both the fault currents and cause tripping

11 KV Incomer tripping alongwith 11 KV Outgoing Due to fault summation at RG-22 Grid.

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Case Study

Tripping Analysis report for 11 KV Mithila Vihar feeder alongwith 11 KV Incomer

Details of Event

11 KV Mithila Vihar feeder tripped alongwith 11 KV Incomer

Observations

oTotal load of the station is around 800 Amps and System is keeping total load on any of the transformer keeping the other transformer on no load.oMithila Vihar feeder tripped on over current High set.o11 KV Incomer-2 tripped on over current High set.oFault data record of the Incomer show’s that Fault seen by 11 KV oIncomer is 9.1 KA while fault seen by Mithila Vihar feeder is 6.2 KA.oIt is observed that Nithari feeder was also seen the fault but not tripped due to isolation of the fault. Protection settings were Coordinated and CT Ratio adoption was found correct.

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Conclusions

After going through the tripping events it was observed that both feeders were getting tripped simultaneously.

After going through the fault data record, it is very clear that fault seen by Incomer is always on higher side as compared to the outgoing feeder.

The tripping in the incomer occurs as the fault current “seen” by the incomer breaker is a summation of the outgoing faults.

It has been learnt from Concerned Zonal staff, that both the outgoing feeders in question, viz. Mithila Vihar feeder and Nithari feeder, are routed on the same poles and on same cross arm. Thereby, the occurrences of birdages in both the feeders occur simultaneously.