Training report on 400/220/132 kV switchyard in India (design and engineering)

Largest power grid in the north India

400 kv Agra substation is one of the most important substation in India and it belongs to the largest power grid in the north India. The whole substation is divided in three parts: 400kV, 220kV and 132kV switchyard.

For 400kv, 220kv and 132kv switchyard a common control room is used Crompton Greaves Limited (CG), an Indian Multinational with manufacturing bases in 8 countries, have signed the contract in 2010 with Uttar Pradesh Power Transmission Corporation Ltd for construction of 765/400 kV Substation at Agra, in Uttar Pradesh.

As we said earlier the whole substation is divided in three parts: 132 kV site, 400 kV and 220 kV site. Other part of project Design, Engineering, Manufacture, Supply, Erection, Testing and Commissioning of Bays will complete by CGL.

In 400/220kv switchyard following outdoor instrument used:

• Two 165 MVA 220/132 kV autotransformer
• Three 315 MVA 400/220 kV autotransformer
• Two 31.5 MVAR shunt reactor
• 15 lighting towers
• SF6 circuit breakers
• Capacitor voltage transformers (CVTs)
• Current transformers (CTs)

In switchyard one room for mulsi fire system and one for generator system is also present. In 400 kV switchyard folowing lines are present for incoming and outgoing power: four 400 kV incoming lines,  three 220 kV outgoing lines and five 132 kV outgoing lines.

SCADA system installed

In SCADA system measured values, i.e. analogue (measured value) data (MW, MVAR, V, Hz Transformer tap position), and Open/Closed status information, i.e. digital data (Circuit Breakers/Isolators position i.e. on/off status), are transmitted through telecommunication channels to respective sub-LDCs.

For this purpose Remote Terminal Units (RTUs) at 400KV, 220KV and few important 132KV substations have been installed. System values and status information below 132 KV have not been picked up for data transmission, except for 33KV Bus isolator position and LV side of generators.

Secondary side of Current Transformers (CT) and Potential Transformer (PT) are connected with ‘Transducers’. The output of transducers is available in dc current form (in the range of 4mA to 20mA). Analogue to digital converter converts this current into binary pulses.

In general, a SCADA system consists of a database, displays and supporting programs.

In UPPTCL, subLDCs use all major functional areas of SCADA except the ‘Supervisory Control/Command’ function. The brief overview of major functional areas of SCADA system is as below:

1. Communications

Sub-LDC’s computer communicates with all RTU stations under its control, through a communication system. RTU polling, message formatting, polynomial checking and message re-transmission on failure are the activities of ‘Communications’ functional area.

2. Data Processing

After receipt of data through communication system it is processed. Data process function has three sub-functions i.e. (i) Measurements, (ii) Counters and (ii ) Indications.

‘Measurements’ retrieved from a RTU are converted to engineering units and linearized, if necessary. The measurement are then placed in database and are checked against various limits which if exceeded generate high or low limit alarms.

The system has been set-up to collect ‘Counters’ at regular intervals: typically 5 or 10 minutes. At the end of the hour the units is transferred into appropriate hour slot in a 24- hour archive/history.

For those statuses which are defined as an ‘alarms’ and the indication goes into alarm, an entry is made into the appropriate alarm list, as well as in the event list and an audible alarm is generated in the subLDC.

3. Alarm/Event Logging

The alarm and event logging facilities are used by SCADA data processing system. Alarms are grouped into different categories and are given different priorities. Quality codes are assigned to the recently received data for any ‘limit violation’ and ‘status changes’.

Alarms are acknowledged from single line diagram (or alarm lists) on display terminal in LDCs.

4. Manual Entry

There is a provision of manual entry of measured values, counters and indications for the important substation/powerhouse, which are uncovered by an RTU or some problem is going on in its RTU, equipment, communication path, etc.

5. Averaging of Measured Values

As an option, the SCADA system supports averaging of all analogue measurements. Typical y, the averaging of measured values over a period of 15 minutes is stored to provide 24 hours trend.

6. Historical Data Recording (HDR)

The HDR, i.e. ‘archive’, subsystem maintains a history of selected system parameters over a period of time. These are sampled at a pre-selected interval and are placed in historical database.

At the end of the day, the data is saved for later analysis and for report generation.

7. Interactive Database Generation

Facilities have been provided in such a way that an off- line copy of the SCADA database can be modified al owing the addition of new RTUs, pickup points and communication channels.

8. Supervisory Control/Remote Command

This function enables the issue of ‘remote control’ commands to the sub-station/powerhouse equipment e.g. circuit breaker trip command.

9. Fail-over

A ‘Fail-over’ subsystem is also provided to secure and maintain a database of devices and their backups. The state of the device is maintained indicating whether it is ‘on- line’ or ‘failed’. There is a ‘backup’ system, which maintains database on a backup computer and the system is duplicated.