Medium-Voltage Systems Commissioning (Above 1 kV to Under 100 kV)

What it is

Medium-voltage system commissioning is a field verification process performed on a complete electrical system rated above 1 kV and under 100 kV before it is first energized and handed over. It is a system-level process rather than an equipment test: the work is organized as a pre-energization phase of some forty-six verifications, an energization phase of sixteen, and a post-energization phase of twelve, each recorded against the project's owner's project requirements, basis of design, drawings, studies, and written energization plan. The record identifies the project, owner, location or substation, system designation, nominal system voltage, and the references for the one-line drawing, the requirements and design documents, and the energization plan. Pre-energization confirms that every piece of apparatus has been acceptance tested under the applicable acceptance standard, that bonding, grounding, safe isolation, clearances, and arc-flash labeling are in place, that instrument transformer circuits, protective settings, logic, firmware, communications, and time synchronization are correct, and that the battery, standby power, and monitoring systems are ready. Energization walks the written plan. Post-energization verifies the system under load and closes out the documentation. NETA ECS-2024 section 7.2 structures these checks so that hazardous or incorrect conditions are ruled out before live voltage is applied.

Why it is performed

At medium voltage the individual equipment tests are already done by the time commissioning starts, and what remains is the class of error no single equipment test can catch: a current transformer circuit with two grounds, a relay whose settings do not match the study it was coordinated from, a differential scheme wired with one polarity reversed, two devices with the same designation on different drawings, or an interlock whose duplicate key is still in a desk drawer. Each of those is invisible in a component report and obvious in a system verification. The phasing is the clearest example: every transformer, cable, and breaker can pass its own test and the bus can still be out of phase with the source it is about to be paralleled with. Commissioning also produces the artifacts the owner has to live with, the as-left setting files, the as-built drawings, the energization date for the warranty, and a written plan that says who does what in which order on the day.

When it is performed

Before first energization, once the equipment acceptance tests are complete and their reports are available for review. The three phases run in order and are not interchangeable: nothing in the energization phase begins until the pre-energization checklist is closed, and the post-energization items, including the insulating fluid and gas analysis, the partial-discharge and thermographic surveys, the loading comparison, and the power-quality survey, are taken after the system has been energized and loaded. The written energization plan is developed during pre-energization and followed step by step on the day. The commissioning report is developed at the end, under the reporting section of the standard.

How it is typically performed

Pre-energization begins with the documents: the owner's project requirements, basis of design, specifications, and regulatory requirements are reviewed, the acceptance test records are reviewed against the equipment ratings and the current drawings, and the drawings, submittals, logic diagrams, settings, and studies are checked for completeness. The physical verifications follow: unique equipment designations, safety and arc-flash labeling, bonding and grounding, provisions for temporary grounding, safe isolation with confirmable open points, clearances, interlocks with duplicate keys accounted for, limit switch sequencing, and the control and interconnection wiring documented through to the supervisory system. The instrument and protection work confirms that current transformer circuits are complete, single-point grounded, never open, with shorting devices positioned, that tap connections match the documentation, that settings, logic, and firmware match the studies, that event recording is synchronized, that communication points reach the end devices, and that the differential and assisted schemes operate. The standby and auxiliary systems, neutral grounding, emergency shutdown, transfer schemes, fluid and gas analysis, valve and tap positions, and the battery system are confirmed, and the as-left setting files, test data, and as-built drawings go to the owner before energization. The energization phase restricts access, secures the exits, removes temporary grounding, sets every switch and test switch per the plan, then follows and documents the plan step by step while the differential operate and restraint values, system phase angle and sequence, equipment phasing, motor rotation, and tap-changer and regulator operation are verified. Post-energization repeats the fluid and gas analysis, establishes the monitoring baselines, verifies the regulatory reports, records the energization date, performs the partial-discharge and thermographic surveys, compares loading with the design, confirms the values reaching protective devices and metering, runs the power-quality survey, and confirms the system functions per the requirements, the basis of design, and the approved sequence of operations.

What gets recorded

The project, owner, location or substation, system designation, nominal system voltage, and the references for the one-line drawing, the owner's project requirements, the basis of design, and the energization plan; the completion of each pre-energization, energization, and post-energization verification, with the exceptions and deferred items noted; the initial energization date, recorded for the warranty transmittal to the owner and the manufacturer; the commissioning report reference; and the ambient temperature, relative humidity, test equipment with calibration due date, comments, and any deficiencies found. The measured results belong to the equipment acceptance test reports and the survey and analysis reports referenced from this record rather than duplicated into it.

How results are evaluated

NETA ECS-2024 section 7.2 publishes no numeric limits or acceptance tables of its own; it frames commissioning as a deterministic verification against the project's own documents. Every apparatus must have been acceptance tested under the applicable acceptance standard and its results found acceptable for energization before the system is energized. Every designation, setting, logic, firmware version, and communication point must match the drawings, the studies, and the sequence of operations. Bonding, grounding, clearances, and labeling must satisfy the applicable standards and codes, and safe isolation must be visually confirmable. Insulating fluid and gas results, partial-discharge and thermographic surveys, and the power-quality survey are judged under their own sections and against the owner's project requirements. Loading is compared with the design criteria. A system is accepted only when every item in the commissioning checklist is confirmed correct with no deferred or provisional items, and the commissioning report, the as-left setting files, and the as-built drawings are in the owner's hands. See the purchased NETA standard for the full checklist and the project documents for the values the checks are made against.