Testing

Industry-leading Testing Capabilities

Our testing capabilities are structured around sound engineering principles and international specifications. This culminates in many non-standard advanced tests being performed on a regular basis in order to ensure full compliance with local, international, or customer specific standards. Our high voltage test facility utilises a custom designed, state of the art SCADA controlled test system. A first in the industry – the high voltage test facility has been remotely accessible for customers since 2019 – allowing customers to view their machine and all its test parameters while being tested, without having to leave their offices.

Standard tests include:

1. Winding resistance:

  • Test measurements are recorded using high accuracy four-wire, high current-capacity resistance bridges

2. Insulation Resistance and Polarization Index:

  • Measured on modern, high accuracy, automated, digital, high current-capacity test equipment
  • This equipment not only measures the insulation resistance value, but also displays the actual test voltage and other parameters such as winding capacitance
  • High current-capacity equipment is critical because low current-capacity measurement equipment will give incorrect readings on larger windings

3. Impulse testing using state of the art Risatti, Baker, P&J brand test equipment:

  • This ensures that any possible inter-turn or inter-phase short-circuits are detected prior to VPI or final test
  • Insulation Resistance testing is ineffective for detecting impending (or developing) inter-turn and inter-phase short-circuits

4. No load testing at rated frequency:
4.1. Values that can be recorded and trended are:

  • Electrical input power (all three phases and individual phases)
  • Power Factor, voltage and current (all three phases and individual phases)
  • Rotational speed
  • Temperature of windings and bearings
  • Temperature of casing or frame
  • Temperature of inlet and outlet air
  • Active and reactive power (all three phases and individual phases)

5. Locked rotor testing (also referred to as short-circuit testing):
5.1. Values that can be recorded and trended are:

  • Electrical input power (all three phases and individual phases)
  • Power Factor, voltage and current (all three phases and individual phases)
  • Temperature of windings and bearings
  • Temperature of casing or frame
  • Temperature of inlet and outlet air
  • Active and reactive power (all three phases and individual phases)
  • Locked rotor torque and current at various supply voltages

Special tests include:

1. Mechanical pressure testing of frames:
This special test ensures the highest level of safety standards on flame proof motors

2. Mechanical load testing at various frequencies:
2.1. Full load testing up to 2000 kW
2.2. These full load tests are not merely quick operating point tests, but full temperature stabilisation can be achieved
2.3. The full load testing facility is frequently used by leading OEMs and other bodies
2.4. This type of testing verifies the full integrity of the repair, design modifications and new designs
2.5. Values that can be recorded and trended are:

  • Electrical input power (all three phases and individual phases)
  • Efficiency: The efficiency can be calculated/measured at various different load points, including full load – as well as various different supply frequencies, supply voltages, etc.
  • Power factor (all three phases and individual phases). The power factor can be measured on all three phases individually and at various different load points, including full load – as well as various different supply frequencies, supply voltages, etc.
  • Voltage and current (all three phases and individual phases)
  • Supply frequency
  • Rotational speed (and slip)
  • Temperature of windings and bearings
  • Temperature of casing or frame
  • Temperature of inlet and outlet air
  • Active and reactive (all three phases and individual phases)

3. Full mechanical load testing:
3.1. This test is also referred to as maximum short-circuit testing or a stall test
3.2. This test evaluates the compliance with various local, international and customer specific
        standards regarding permissible locked rotor times.
3.3. Values that can be recorded and trended are:

  • Electrical input power (all three phases and individual phases)
  • Power Factor (all three phases and individual phases)
  • Supply frequency
  • Rotational speed (and slip)
  • Temperature of windings and bearings
  • Temperature of casing or frame
  • Temperature of inlet and outlet air
  • Active and reactive (all three phases and individual phases)
  • Locked rotor torque and current at various supply voltages

4. Pull-out torque testing:
4.1. The Pull-out torque test is also referred to as maximum overload testing
4.2. This test evaluates the compliance with various local, international and customer-specific standards regarding permissible overload or pull-out torque
4.3. Values that can be recorded and trended are:

  • Electrical input power (all three phases and individual phases)
  • Power Factor, voltage and current (all three phases and individual phases)
  • Supply frequency
  • Rotational speed (and slip)
  • Temperature of windings bearings
  • Temperature of casing or frame
  • Temperature of inlet and outlet air
  • Active and reactive power (all three phases and individual phases)
  • Reactive power (all three phases and individual phases)
  • Shaft torque

5. Remote Web Access Testing Facility:
M&C’s high voltage test facility at its Cleveland, Johannesburg, centre of excellence – has implemented a remote web access facility for its customers since 2019. This allows customers to perform customer witness tests (and other relevant tests) completely remotely, without leaving their place of work. This allows the machine under test to be viewed via a video feed, and all test parameters visible to the M&C test technicians also remotely visible live throughout the test duration. All that is required is an internet connection and a web browser. M&C lead the way in the industry with this convenient, safe and cost-effective service.

6. Tan Delta testing:
This test is used on new and service-aged windings to determine insulation condition. It is employed on new and rewound windings of 3.3 kV and higher, to ensure that manufacturing processes such as winding and VPI are correctly implemented. It is more correctly referred to as dielectric dissipation factor Tan Delta testing in Europe, or Power Factor tip-up testing in the U.S.A and South America.

7. Partial Discharge:
This analysis method assesses the insulation condition of high voltage (4 kV and higher) windings by statistically measuring the partial discharge activity of the winding, and displaying it superimposed on the main supply voltages. The method uses predominantly capacitive terminal couplers, and although it can be used off-line – its main use industrially is on-line. Partial Discharge analysis has the potential capability to identify locations and types of partial discharge sources.

8. Stray Flux (or Rotor Flux) Analysis:
This method of measuring the instantaneous magnetic flux at a point location in the airgap of synchronous rotating machines allows the detection of short-circuited turns in the rotor. It is very effective on cylindrical rotor (two pole) alternators and motors, but also effective on salient pole rotor motors and alternators – with the effectiveness depending on the number of turns per pole. Its main advantage is that it can be performed on-line with no intrusion to the machine operation. As such – it assesses short-circuited turn probability while the rotor is rotating at rated speed, when centrifugal forces are at their normal levels (unlike the RSO/ RSG test which is normally done at standstill).

9. Magnetisation assessment / Degaussing / Demagnetising:
Magnetisation of certain components in a rotating drive-train (electrical or mechanical drive-trains) can cause severe shaft currents that flow through bearings, gears and other components. These currents have the potential of destroying components within minutes (even seconds). M&C has the capability and equipment to both measure the magnetisation / gauss levels on drive-trains and individual components – and to demagnetise affected components to prevent subsequent damage.

10. Recurrent Surge Oscillograph / Graph (RSO / RSG):
This test determines the likelihood of short-circuited turns by the surge comparison method. It is usually performed on two pole cylindrical rotors while stationary – and it is most effective on such rotors. It can be performed on other rotor types and pole numbers – with less accuracy or effectiveness. It can also be performed on running machines where there is access to the field winding terminals (slip-ring excited rotors or rotors with telemetry systems). The test compares two identically generated pulsed voltage waveforms, when applied with opposite polarity to the terminals of synchronous machine rotors.

Load Testing Facilities
We proudly operate seven machine test facilities in South Africa and abroad:

1. High-voltage AC:

  • Full mechanical load testing up to 2 MW

2. DC and Traction:

  • Full mechanical load testing up to 600 kW

3. LV and Flameproof:

  • Two full mechanical load testing facilities of up to 750 kW

4. Transformers:

  • Up to 33 kV

Site load conditions are simulated. This gives our customers full confidence in the repair, and it also provides excellent technical information that can be used in engineering and commercial decisions regarding the operation of the transformer.

Typical results that can be obtained that are important for transformer power consumption calculations and can result in power savings through transformer design changes or replacements:

  • Losses (efficiency), resistances, impedances, equivalent circuit, etc.
  • Can be used in fault finding and diagnostics
  • Temperature rise of windings (can be used to determine the suitability of the transformer for application and loading level)