Category Archive for: «Testing and Commissioning»

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Testing of Power Transformer – Measurement of Zero-Sequence Impedance

Earth-fault protection Purpose of the measurement The zero-sequence impedance is usually measured for all star-connected windings of the transformer. The measurement is carried out by supplying a current of rated frequency between the parallell connected phase terminals and the neutral terminal. The zero-sequence impedance per phase is three times the impedance measured in this way. […]

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Why is Continuous On-line Monitoring of Partial Discharge in the Switchgear Necessary?

What’s the condition of your switchgear? Not sure? You know that periodical maintenance test like partial discharge test can still leave switchgear in virtually unknown condition. Insulation defects and deterioration may very well develop in service within maintenance cycle. These defects are often not detectable with traditional off-line tests and yet, traditionally, on-line or off-line […]

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How to measure insulation resistance of a motor

Winding insulation resistance If the motor is not put into operation immediately upon arrival, it is important to protect it against external factors like moisture, high temperature and impurities in order to avoid damage to the insulation. Before the motor is put into operation after a long period of storage, you have to measure the […]

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Erection Procedures of Earthing Arrangements (TNC, TN-S, TNC-S and TT)

Earthing of low voltage networks The earthing of low voltage networks in the UK is largely determined by the Low Voltage Supplies. However, if the incoming supplies are at 11kV and the transformers are in the ownership of the user, the LV supplies may be earthed in a less conventional way using a high impedance. […]

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Inspection and Test procedures for Instrument Transformers

Procedures to follow: Visual and Mechanical Inspection Electrical Tests: Electrical Tests – Current Transformers Electrical Tests – Voltage Transformers Electrical Tests – Coupling-Capacitor Voltage Transformers Electrical Tests – High-Accuracy Instrument Transformers (Reserved) Test Values: Test Values: Visual and Mechanical Test Values: Current Transformers – Electrical Test Values:Voltage Transformers – Electrical Test Values: Coupling Capacitor Voltage […]

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Testing of power transformer – Measurement of impedance voltage and load loss

Purpose of the measurement The measurement is carried out to determine the load-losses of the transformer and the impedanse voltage at rated frequency and rated current. Apparatus and measuring circuit On Figure 1 above (Circuit for the impedance and load-loss measurement) there are following figures: G1 – Supply generator T1 – Step-up transformer T2 – […]

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Testing Procedures for HV Voltage Transformers

Content: Equipment required for testing General inspection Insulation Resistance Test Polarity Test Transformer Turns ratio test 1. Equipment required Following equipment is necessary to perform testings: Polarity test kit Megger 500-5000V Ohmmeter Multimeter Autotransformers & Step-up transformers Go up to the Content 2. General inspection Mechanical checks General visual inspection and compliance with the drawings […]

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Inspection and test procedures for Rotating Machinery, Synchronous Motors and Generators

Procedures (Index) Visual and Mechanical Inspection Electrical Tests Test Values Visual and Mechanical Tests Electrical Tests Pictures: Electrical machine wired for electrical testing The Electrical Machines Laboratory TABLE 100.10 – Maximum Allowable Vibration Amplitude TABLE 100.12 – US Standard Fasteners 1. Visual and Mechanical Inspection Compare equipment nameplate datawith drawings and specifications. Inspect physical and […]

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Power Transformer Capacitance and Dissipation Factor Test

Transformer insulation system The capacitance and dissipation factor test is an AC low voltage maintenance test and is very similar to the power factor test. While the transformer preparation is identical to the power factor test procedure, there is no requiremnts to make connection changes once the initial test set connections are made. High-voltage winding […]

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Power Transformer Turns Ratio Test

Turns ratio between the windings The turns ratio test is an AC low voltage test which determines the ratio of the high voltage winding to all other windings at no-load. The turns ratio test is performed on all taps of every winding. Voltage is applied on the H marked leads and measured of the X […]

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