Medium-Voltage Switchgear and RMU Testing

What it is and when you need it

Testing and commissioning of medium-voltage switchgear confirms that each panel arrived and was installed undamaged, that its switching devices open and close as the manufacturer states, that the interlocks prevent dangerous operations, and that the relay trips the breaker it is meant to trip. It applies to air-insulated medium-voltage switchgear with withdrawable breakers, to compact gas-insulated switchgear, and to RMUs (Ring Main Units) in distribution rings.

It is needed before the first energization of a substation, an industrial plant or a solar plant transformer station, and also when a switchboard is extended, a panel is relocated or a breaker is replaced. In solar plants every transformer station has its switchgear, and the medium-voltage collector network depends on all of it operating and interlocking correctly: a fault in one panel takes a section of the plant out of service.

What is included

Inspection and mechanical verification

Installation inspection, busbar and cable connections, grounding and the condition of the enclosure.
Gas pressure or density indicator in gas-insulated panels and RMUs.
Manual and electrical operation of each device, position indication and spring charging.

Electrical tests

Insulation resistance of the main circuit and the auxiliary circuits.
On-site dielectric test at the value and waveform set by the manufacturer.
Contact resistance of the main circuit.
Opening and closing operating times of the breaker and pole simultaneity.
Current transformers of the panel: ratio and polarity.

Interlocks and control

Interlocks between breaker, disconnector, earthing switch, truck and doors, per the manufacturer’s scheme.
Voltage presence indicating system.
Local and remote commands, signals and alarms to the control system.

Panel protection

Secondary injection of the relay with the approved settings, including self-powered relays.
A real breaker trip from the relay and, where applicable, from the transformer protection.

How we work

Information review. Manufacturer’s manual, control drawings, interlock scheme, approved settings and factory test values. We agree with you which tests the manufacturer performs and which ones we do.
De-energized tests. With the panel isolated and grounded, we carry out the inspection, operations, insulation, dielectric test, contact resistance and timing, using calibrated test equipment from recognized manufacturers (OMICRON, Doble, Baur, among others).
Protection and control. We test the relay with the Omicron CMC 356, the real trips and every interlock, also attempting the operations that must remain blocked.
Energization. We attend the first energization following the project sequence and verify voltages, phase sequence and signals.
Test record. One record per panel with the measured values, the reference value and the result.

This work is part of our testing and commissioning service. The circuit breaker of the step-up substation is tested as described in circuit breaker testing.

Standards and criteria for medium-voltage switchgear testing

IEC 62271-200 is the product standard for metal-enclosed switchgear above 1 kV and up to 52 kV, and provides for tests after installation on site. IEC 62271-1 sets the common specifications, IEC 62271-100 covers circuit breakers and IEC 62271-103 covers switches and switch-disconnectors. Voltage detecting systems follow IEC 62271-213. Local electrical codes generally require interlocks between the switching and isolating devices.

Most acceptance criteria come from the manufacturer: the on-site dielectric test value, the maximum contact resistance and the operating times are compared with the manual and with the factory protocol of each panel. When no reference exists, the first test record becomes the baseline for maintenance tests.

Switchgear and RMUs from many manufacturers, European and Asian, are now on the market. The tests are the same in all cases; what changes is cable access, how the gas is checked and the interlock sequence, which we always take from the manual of the installed model.

What you receive

A record per panel with inspection, operations, insulation, dielectric test, contacts and timing.
A relay record for each panel and a backup of the settings loaded.
A list of verified interlocks, including the blocked operation attempts.
Signals and commands verified with the control system.
Comments and recommendations on anything that does not comply, before energization.

Why Tiza Group

A single technical lead for the panel, its relay and its integration with the control system.
Experience in medium, high and extra-high voltage, in substations, industry and solar plants.
Test equipment from recognized manufacturers (OMICRON, Doble, Baur, among others) for primary and secondary tests.
Experience with relays from the main brands: Siemens, Schneider Electric, SEL, ABB, GE, Fanox, NOJA Power and Efacec.

We do field work in Colombia, or elsewhere on request. Tell us about your project.

Frequently asked questions

What is the difference between testing a circuit-breaker panel and an RMU?

In a circuit-breaker panel, withdrawable or fixed, we test the breaker's timing and contact resistance, the operating mechanism and the truck. In an RMU, almost always gas-insulated, the load-break switches and the breaker or fuse-switch combination sit inside a sealed tank: we check the gas indicator, the operation of each function and the cable connections, without opening the tank.

What voltage is applied in the on-site dielectric test?

IEC 62271-200 provides for dielectric tests after installation at a fraction of the factory withstand voltage. The value, the waveform and the connection point are set by the switchgear manufacturer in its manual. We follow that value and record it in the test protocol.

Do you also test the panel relay?

Yes. We verify the relay by secondary injection with the approved settings, including the self-powered relays of RMUs, and check that each protection trips its own breaker. If the relay arrives without settings, we configure it too.

Is this service useful for the transformer stations of a solar plant?

Yes. The medium-voltage switchgear is one of the parts of the transformer station, together with the transformer and the auxiliary services. We test it as part of the plant commissioning or as separate work if you have already contracted the rest.

Must the switchgear be de-energized for testing?

Yes. Tests are done with the panel de-energized, isolated and grounded, under the lockout and permit procedure set by the person responsible for the installation. Live tests are limited to energization and checks under load.

Need it for your project?

Send us the single-line diagram, the equipment list and your target date, and we will reply with scope and schedule.

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