Part-1 Purpose of Winding resistance measurement test of transformer in English

Welcome back dear Knowledge seekers. We will discuss one by one reasons that create situation for conducting this test. 

This is one of the major test of transformer which is included in type test, routine test and field test of transformer. Type test is required for particular design of transformer by manufacturer for confirming product design in use. Routine test is required on every transformer for its construction healthiness and operational performance and field test is required on every transformer before putting into service and for regular maintenance purpose.

This test is useful to identify any damage of transformer winding which can be during time of manufacturing, transporting, erecting, commissioning or maintenance. Manufacturing needs different kind of work upon transformer so after it is required to check healthiness of winding. During transportation and erection-commissioning also there may be chance of winding damage as during transportation, transformer may subject to jerks and vibration. During erection-commissioning is also chance of winding damage as during these works transformer is lifted, put on foundation and manpower may make mistake while working with inside parts of transformer. Maintenance work is also the same case as erection-commissioning for requirement of the winding resistance test.

Detection of deterioration of tap changer contacts and problem in tap changer mechanism can be found by this test. For the transformer with tap changers, current injection path to the windings goes via tap changer so if deterioration is there, the resistance measurement will be abnormal and we will come to know about it. Now a days test kit senses the decrement in current injection during changing tap of transformer so if the current decrement is large, the test kit will stop it self and we will come to know about problem in tap changer mechanism while changing the tap. 

Detection of open or loose connection of winding with bushing, shorting of phase, broken strands can be identified by this test. By measuring the resistance of each winding, we can assure that connections are properly connected and tight. Winding resistance measurement is useful for calculation of I2R loss and winding temperature rise test.

Impact Recorder use for Power Transformer

In the above picture is shown image of impact recorder for reference which is mounted on power transformer body.

1. During transportation of Power Transformer from manufacturing company to installation site, it experiences mechanical vibrations and shocks.
2. Due to this there are chances of damage like winding and core damage, inter turn insulation damage which can cause short circuit, looseness of clamping, low clearance between tank and active part, loss of nitrogen from tank etc.
3. This type of damage can be identified by using the measured values of impact recorder before starting commissioning of Power Transformer.
4. Electronic impact recorder store the values digitally with date and time so it provide additional information.
5. Accepted values of impact recorder is multiplication of “g” where g= 9.8 m/s2 like 0.4g.
6. Values are measured in three axis like direction of placement, perpendicular direction of placement and vertical direction of placement of transformer.
7. Accepted impact values differ for different sized power transformers and impact recorder is generally used for high MVA power transformers.
8. If the measured values are more than acceptable limits than internal inspection and various testing need to done on transformer and it further goes to on site or factory repairs upon severity of damage.

Same content to understand by video on my YouTube channel at https://youtu.be/brpVGQi9imw

Testing of Switchgear - Part 3 (Breaker operating timing test )

In previous blog, I discussed for Breaker Contact Resistance Measurement (CRM test) for switchgear. We will discuss further test in this post.

The next test we will discuss is as below.

Breaker Operating Timing Test

Purpose of the test :  

Circuit breaker is a part in electrical system which separates faulty part in event of fault. The separation time of the faulty part must be minimum and circuit breaker should do this quickly. This timing is called breaker operating time in which it removes the faulty part from system. Inside the breaker, it operates through mechanical operation. If this mechanism has any abnormality, then it will not operate smoothly and the breaker operating time will be more. When there is fault in the system, there will be high currents in the power circuit. Every equipment is designed to sustain for large current for very short time considering that circuit breaker will operate and will remove the fault from the system. If the circuit breaker will not operate within its desired time during the fault, there will be heavy damage to electrical equipment due to high currents. So we are checking the breaker closing and opening time through this test to ensure normal breaker timings.

Breaker Operating Time: Breaker operation time is total time of breaker closing time and opening time.

Breaker Opening Time: Breaker opening time is time between charging of tripping coil to separation of fixed and moving contact of breaker.

Breaker Closing Time: Breaker closing time is time between charging of closing coil to joining of fixed and moving contact of breaker.

Testing of Switchgear - Part 2 (Breaker Contact Resistance Measurement test)

In previous blog, I discussed for insulation resistance test for switchgear. We will discuss further test in this post.

The next test we will discuss is as below.

Breaker Contact Resistance Measurement (CRM test)

• Why we are carrying this test?

We are conducting this test to find the resistance of breaker contact where moving contact and fixed contact meet each other. This contact resistance should be low because the circuit breaker is carrying high current. So if the resistance of contact will be high, there will be more energy loss (more I²R) losses and it can’t pass high currents. By carrying this test, we come to know about looseness in contact, corrosion present at contact surface or any other contamination in the contact. This test shows healthiness of the contact.

• How to measure contact resistance of breaker ?

We are using one kit called CRM 100 for the test. This test works upon method of 4 wire Kelvin DC voltage drop test. In this method 4 wires are used for resistance measurement. Two wires are used for current injection and two wires are used for voltage measurement. In this method the current amount is set to high like 100 Amps. Higher the current we inject, more accurate resistance we get. Two current leads and two voltage leads are connected across each breaker pole. The resistance here we will get in terms of 20 micro ohms. All three breakers pole resistance should be same. Here the resistance value we obtain, depends upon capacity/ voltage rating of the breaker.

We will discuss further test in next blog for Breaker Operating Timing Test.