Generator Maintenance Guide / 03

Generator Electrical Checks: ATS, Switchboard and Load Testing

A generator that starts is not enough. ATS switching, low-voltage switchboards, grounding, cables, breakers, paralleling controls and load tests all need regular checks and records.

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01 ATS automatic switching View content 02 Low voltage distribution cabinet View content 03 Load testing View content 04 Parallel system View content

Applicable scene

For mine sites with ATS switching, paralleling, complex low-voltage distribution, dewatering backup or frequent trips.

Many sites understand maintenance as engine maintenance, but ignore the power transmission and distribution links after the generator output. Low-voltage power distribution cabinets, circuit breakers, cables, grounding, ATS automatic switching, parallel cabinets and controllers. If any link is unstable, critical loads may not be able to receive power.

Non-professionals on site should not dismantle or modify electrical equipment. Daily work should stay with observation, records, cleaning, and confirming power-off plus lockout/tagout before tightening. Abnormal signs should be handed clearly to electrical staff or engineers for diagnosis.

Terminals, grounding and cables

Check the control cabinet, output cabinet and cable terminals for signs of looseness, blackening, odor, overheating or moisture.
Check whether the ground connection is complete and whether the ground wire has been affected by construction, transportation or corrosion.
Observe whether the cable path has been run over by vehicles, soaked in water, worn on sharp edges, or has too many temporary joints.

ATS switching and backup circuit

Confirm that the ATS is in the correct mode and that the automatic/manual status meets the operating requirements for the day.
Regularly record switching test results, including main power loss, generator starting, load transfer and switchback processes.
Check whether critical loads are actually connected to the standby circuit. Don’t judge only by the presence of a standby generator set on site.

Paralleling and load testing

When multiple generator sets are paralleled, record the load distribution, frequency, voltage, and alarm status of each generator set.
Regularly conduct actual-load or staged-load tests so the standby generator set is not only started without load for long periods.
Pay attention to voltage drops, frequency fluctuations and protection actions when starting large motors.

Execution steps

When site staff follow the same inspection steps, engineers can diagnose from the same facts.

Maintenance actions must be performed repeatedly and evidence must be left. The following steps are suitable as the basic process before team handover and repair report.

Confirm safety requirements first

Before entering the electrical cabinet, terminals and ATS for inspection, qualified personnel should perform power outage, power inspection and lockout and tagout. Routine inspection personnel are mainly responsible for appearance, sound, temperature rise and records.

Verify switching logic with repeatable tests

Backup power should be tested before a real outage. Test ATS and critical-load transfer on schedule, then record start time, transfer time, return-transfer status, and abnormal alarms.

Review trips together with load changes

If tripping occurs when the crusher, water pump, or air compressor starts, do not check only the circuit breaker itself; also review the starting method, cables, protection settings, and generator-set capacity.

Exception signal

In these cases, do not simply reset the alarm and keep running

The electrical cabinet smells burnt, generates heat, terminals are discolored, or cable insulation is damaged.
The generator was able to start during the ATS test, but the critical load was not transferred.
The standby generator set has only been started without load for a long time and has never carried actual critical loads.
In a paralleling system, one generator set carries a much higher or lower load, but the alarm is never reviewed.

Record list

Keep these records for every inspection and service request

ATS test date, mode, startup time, switchover time, switchback time and results.
List of critical loads, actual load test load rate and voltage frequency changes.
Photos of terminals, grounds, cables, control cabinets and circuit breakers.
The load, alarm code, protection action and recovery method before and after each trip.

How engineers can assist

Complete records speed up remote diagnosis and make any site visit more effective

If alarms, trips, starting difficulties, abnormal voltage, abnormal fuel consumption, or unstable loads have occurred on site, please give priority to retaining controller photos, fault videos, operating hours, recent maintenance records, oil status, load lists, and ATS/power distribution photos.

When it comes to ATS, generator paralleling systems, low-voltage distribution cabinets and protection settings, single-line diagrams, cabinet photos, controller alarms and test videos should be provided.
If critical-load switching fails, describe the main source, backup source, ATS model, load circuit and site operating procedure.
If frequent trips occur, equipment starting methods, cable distances, circuit breaker specifications and load change records should also be provided.

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