Guidelines for inspecting, testing, and start up substation and Medium Voltage switchgear

Substation Breakdown

Somewhere in the globe, a petrochemical facility experiences a big electrical breakdown on a daily basis. Equipment is usually back up and running again after a short investigation into and correction of issues like corrosion, heat buildup, insulation failures (often hastened by pollution or humidity), animals, poorly planned terminations, or mis-operation. The extent of damage is typically limited when protection systems are appropriately planned, implemented, and maintained.

A comprehensive examination and inquiry may be necessary to determine the cause in circumstances involving substantial and potentially collateral damage. Regrettably, there is never an enticing conclusion. In many cases, the apparatus or a system was flawed in some way, either in its design or its installation, or in its functionality.

In addition, many failures have an unidentified or unclear reason. When things didn’t work out the way we expected, there are two main reasons:

1. Inadequate maintenance
2. Wrong installation

It takes a lot of work, documentation, and planning to commission a medium voltage switchgear or substation safely and on time. It is common practice to assemble and test new switchgear at the plant.

A lot of the time, though, the electric system was well-planned and built with good intentions, but it wasn’t tested and examined by experts before it was put into operation.

The testing and inspection procedures that must be followed before or after energizing medium voltage switchgear and substation equipment are outside the scope of this study. When it comes to substation or medium voltage switchgear protection systems, though, it does cover a lot of ground to make sure they’re electrically suitable for service.

What follows is a discussion of:

1. Critical factors to think about while strategizing the commissioning
2. Common commissioning mistakes and how to avoid them
3. Practical ways for testing protective device circuits

Protective Device Circuit Tests

DC Control Circuits

We evaluate DC control circuits to make sure that circuit breakers and other switching devices respond properly to all control signals and that panel lights and graphics on distant control room monitors work as intended. Functional testing should be used to verify the following control devices and operations:

• Control switch trip and close functions and associated indicating lights
• Protective relay tripping
• Automatic transfer schemes
• Lock-out relays and electrical interlocks
• Local, remote, and supervisory (SCADA) control and indication

Figure 1 – Simplified DC trip circuit schematic

Errors in DC control circuits can be identified through functional tests. The first step of these functional tests is to ensure that the wiring is accurate. They continue until all of the logic strings, or more precisely, all of the control devices, have been tested and found to be functioning. This could seem like a daunting and time-consuming operation when confronted with a complex DC schematic for a circuit breaker.

Nevertheless, it is essential that the testing and inspection be carried out in a safe manner without endangering any equipment.

The following factors need to be taken into account for this to be achieved:

1. the source of the equipment
2. the risk of relay failure
3. unintended functioning of circuit breakers

Less care may be required with the interior wiring of newly manufactured and extensively tested equipment. You can’t assume that equipment is service ready if it has been correctly installed in the field because not all vendors have sufficient quality standards. Verifying connections made after field installation can take precedence over factory tests if the equipment comes from a “trusted” source or if they were observed.

Particular caution and a thorough examination of all internal connections are required prior to the application of control power in the case of equipment that has undergone substantial modifications or has been acquired without testing.

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