Commissioning (PNR): what it is, stages, scope of work

Author: Viacheslav Yurdyk, Quality Engineer at LK Energy Group.
Responsible for quality control at the switchgear manufacturing facility and on site after electrical installation work: factory testing of NKU assemblies, participation in commissioning and verification of electrical laboratory test reports.

Commissioning (PNR) is a set of tests, measurements and adjustments performed on installed electrical equipment after the electrical installation work is complete and before the electrical installation is put into service. The purpose of commissioning is to confirm with instruments that the equipment has been installed in accordance with the design, that its parameters meet the applicable standards (PUE in particular), that the protective devices operate correctly and that the installation is ready to run safely under load. The output is a set of test reports and a technical report from the electrical testing laboratory, which are required for acceptance of the installation into service.

What commissioning is and how it differs from installation work

Electrical installation work answers the question “has it been assembled”, while commissioning answers “does it work correctly”. The installation contractor lays the cable lines, assembles the switchboards and connects the equipment. The commissioning engineer then checks the circuit diagram, measures parameters with instruments, energises the equipment in accordance with the test programme and records the results in test reports.

Installation work that looks flawless can still hide defects that only instruments reveal: reduced insulation resistance in a cable damaged during laying; a swapped phase sequence; a circuit breaker that will not clear a short circuit within the specified time because the “phase–neutral” loop impedance is too high. That is why commissioning is a distinct type of work with its own methodology, instruments and documents, rather than “the last day of installation”.

Stages of commissioning

Established engineering practice divides commissioning into four stages — from studying the design documentation to running the equipment under load.

Stage	What is done	Stage output
1. Preparation	Study of the design and manufacturer documentation, development of the commissioning programme, preparation of instruments and test report forms	Commissioning programme, agreed work schedule
2. Work with no voltage applied	Visual inspection, check that the installation matches the design, insulation resistance measurement, verification of circuit connections	List of findings, first measurement reports
3. Individual tests with voltage applied	Adjustment of individual devices: circuit breakers, PZV, AVR, relay protection, phasing of incomers	Test reports for each item of equipment
4. Integrated commissioning	Verification of the combined operation of all equipment in normal operating modes under load	Commissioning completion certificate, technical report

In practice, the second and third stages often run in parallel with the completion of installation work on individual sections. This is a normal way to organise the work — provided that each section goes through its full test cycle.

What the scope of commissioning includes: typical tests and measurements

The exact scope is defined by the design and by the PUE acceptance test standards. For a typical switchgear assembly the list looks as follows:

insulation resistance measurement of cables, wiring and equipment windings using a megohmmeter;
earthing system resistance measurement and bonding continuity checks — continuity of protective conductors;
measurement of the “phase–neutral” loop impedance — to confirm that the protective device will disconnect the line within the specified time in the event of a short circuit;
primary current injection testing of circuit breakers — the actual tripping current and time are compared with the manufacturer's characteristic;
PZV testing (residual current devices) — tripping current and time;
phase sequence check and phasing of incomers and sections;
adjustment of automation circuits — AVR, control circuits, signalling, interlocks;
for installations above 1 kV — increased-voltage withstand testing, checks on power transformers (transformation ratio, winding resistance, vector group) and adjustment of relay protection and automation (RZA).

Regulatory basis. For new electrical installations, the scope and limits of testing are set by the PUE (the chapter “Acceptance test standards”); for subsequent operation, by the Rules of Technical Operation of Consumer Electrical Installations (PTEES). The commissioning programme is drawn up on exactly this basis: every item in the programme has its corresponding test report.

Who carries out commissioning and which documents the customer receives

The tests and measurements are performed by an electrical testing laboratory — a certified unit with calibrated instruments and personnel holding the appropriate electrical safety qualification group. A “technician with a multimeter” cannot issue a test report: the results are recognised during acceptance only when the laboratory is certified and the instruments have passed calibration.

On completion of commissioning, the customer receives a package of documents:

test and measurement reports — a separate report for each type of work, stating the instruments used, the conditions and the values obtained;
technical report of the electrical testing laboratory — a compilation of the test reports with a conclusion on the compliance of the installation with the PUE requirements and the design;
commissioning completion certificate — the administrative document for acceptance of the facility;
where required — a defect list covering issues found during testing, to be rectified by the installation contractor.

This package is needed when the electrical installation is accepted into service and becomes the baseline for subsequent periodic operational testing.

Why commissioning matters to the customer

Hidden defects are found before voltage is applied. Damaged cable insulation, swapped phases, a disconnected protective conductor — all of this is visible to instruments, not to the eye.
Verified protection. A circuit breaker only protects when its characteristic is matched to the actual “phase–neutral” loop impedance. Commissioning verifies this by measurement rather than by assumption.
Documents for acceptance. The test reports and the technical report form part of the package reviewed during connection and acceptance of the facility into service.
A recorded initial condition of the installation. With the commissioning test reports on hand, the operations team can see how parameters change over the years and plan maintenance on a sound basis.

One practical note: friction is lowest when the installation work and the commissioning are handled by a single contractor. In that arrangement the commissioning engineer checks the work of “his own” installers, defects are rectified as part of the routine, and the customer receives one package of documents and one area of responsibility — without disputes between the installation contractor and the laboratory over whose defect it is.

Frequently asked questions

What is commissioning (PNR) in simple terms?

It is an instrument-based check of installed electrical equipment before start-up: insulation and earthing are measured, protective devices are tested, automation is adjusted and the results are recorded in test reports. Put simply, it confirms that the installation is not merely assembled, but works correctly and safely.

Is commissioning needed if the installation work was done well?

Yes. The PUE acceptance test standards require measurements and tests for new electrical installations regardless of how well the installation work was done, because some parameters — insulation resistance, the “phase–neutral” loop, protection tripping times — cannot be checked visually.

What determines how long commissioning takes?

The equipment involved: the number of cable lines and circuit breakers, the presence of AVR, relay protection, and equipment above 1 kV. For a small switchboard it may be a single laboratory visit; for a switchgear assembly with several sections and automation it is a separate stage in the construction schedule. The duration is fixed in the commissioning programme and schedule before work begins.

How does a test report differ from a certificate?

A test report records the results of a specific measurement: what was measured, with which instruments, the values obtained and whether they meet the standard. A certificate confirms the completion of the work as such. The laboratory's technical report combines the individual test reports and gives an overall conclusion on the installation.

LK Energy Group carries out electrical installation work and commissioning with electrical laboratory testing — from insulation resistance measurement to integrated commissioning of switchgear assemblies, with a full package of test reports. If installation work is nearing completion at your facility and you need testing and test reports — get in touch with us.

What commissioning (PNR) is: stages and scope of work