Page 447 - Industrial Power Engineering and Applications Handbook

Testing of metal-enclosed switchgear assemblies 141421
14.1 Philosophy of quality systems Power frequency voltage withstand or HV test on
power as well as control and protective circuits
This has been covered in Section 11.1 Impulse voltage withstand test for system voltages
2.4 kV and above
3 Temperature rise limits (or rated continuous current
14.1.1 Quality assurance capacity)
To fulfil quality requirements, the material inputs going 4 Short-circuit strength
into the making of assemblies such as MS sheets (for 5 Momentary peak or dynamic current
their surface finish, thickness and bending properties), 6 Protective circuits
hardware (for their correct sizes, quality of threads and 7 Clearance and creepage distances
tensile strength etc.), busbars and cables (for their area 8 Degree of protection:
Enclosure test
of cross-section, conductivity and quality of insulation
in the case of cables), insulators and supports (for their Weatherproof test
sizes and quality of SMC, DMC or any other material 9 Mechanical operation.
used), and all other switchgear components such as
breakers, contactors, switches, fuses, CTs, PTs and meters 14.2.2 Routine tests
etc. (for their ratings, duty class, class of accuracy Routine tests are conducted on each completed assembly,
(wherever applicable) and specifications etc.) must be
properly checked and recorded, according to the irrespective of voltage, current, fault level and construc-
tional details and whether it has already undergone the
manufacturers; internal quality checks and formats. type tests. The following steps will form routine tests:
This should be carried out before they are used in
assemblies to eliminate any inconsistency in a material
or component. 1 Checking for any inadvertent human error during
Similar stage inspections are necessary during the course assembly.
of manufacturing to assure quality at every stage and This check may be carried out both at the works,
eliminate any mistakes in construction, assembly or after final assembly, and at the site after the installation
workmanship during the course of manufacturing. Thus, before conducting routine tests or energizing the
a product of desired specification and quality is ensured. assembly. The checks can be carried out at a lower
voltage to detect any shorting links or spanners left
inadvertently on live terminals, weak insulation or
14.1.2 Purpose of testing insufficient clearance or creepage distances between
The purpose of testing a switchgear or a controlgear the phases or phase to ground conductors. In the case
assembly is to assure its compliance with the design of a defect the same must be rectified immediately.
parameters, material inputs and manufacturing consis- 2 Inspection of the switchgear assembly to check the
tency. Here we discuss this for a switchgear assembly following:
only. For tests on a controlgear assembly, the relevant General arrangement and appearance
tests may be chosen from those prescribed for a switchgear Mechanical operation of all movable parts and
assembly. interlocks
Random checking of bolted connections for proper
jointing and tightening
14.2 Recommended tests Generally all important requirements as discussed
in Section 13.4 that may have been required in the
specifications of the switchgear or controlgear
The following are the recommended tests according to assembly.
IEC 60439- 1 for LT, IEC 60694, IEC 60298 for HT and 3 Inspection and verification of electrical wiring:
ANSI C-37/20C for LT and HT switchgear assemblies For power connections
that may be carried out on a completed switchgear For controls, metering and sequential operations if
assembly. any
For protective circuits
14.2.1 Type tests For grounding of instrument transformers
For checking the insulation of the control wiring
Type tests are conducted on the first enclosure of each
voltage, current rating and fault level to demonstrate For a polarity test of CTs.
compliance with electrical and constructional design 4 Verification of insulation resistance or measurement
parameters. The tests provide a standard reference for of the leakage current, both before and after the
dielectric test.
any subsequent enclosure with similar ratings and 5 Verification of dielectric properties, limited to power
constructional details. The following tests may be
conducted to demonstrate verification of the following: frequency voltage withstand or HV test on power as
well as control and protective circuits.
I Insulation resistance or measurement of leakage
current, both before and after the dielectric test 14.2.3 Seismic disturbances
2 Dielectric properties: In Section 14.6 we provide a brief account of these