Tests On Electrical Machines Before Commissioning

 

Roles Of Bureau Of Indian Standards 

In Testing of Electrical Equipment Indian National institute i.e. Indian standard Bureau specifies the standards for particular machines apparatus, equipments material and so many engineering items.

Newly manufactured machines by a factory or firm has to undergo specified testing. measurement etc. As the norms fixed by this institute to get the certification or ISI marks.

This certification is a must in some cases and customers are sure of quality of the machines as it has undergone the tests as per ISI. 

So roles of Bureau to pass and certify the machines equipments/Apparatus which have undergone the standard tests decided by their institution.

Objectives Of ISS

1. To specify standards for machines, equipment, apparatus, materials etc. 
2. To suggest standard tests for newly manufactured machines.
3. To specify the plus/minus limits for the test results. 
4. To specify the tolerance to accept the items. 
5. To give ISS certification.

Tests On Electrical Machines Before Commissioning

Before carrying out the tests as per ISI standards some primary tests are carried out at the site by external and superficial examination of the machine as follows:

(A) Mechanical Tests

1) Read the data printed on the name plate and check the same for the machine.

2) See that all the parts are in position and all the accessories are available and no parts are missing. See also the compactness of the machine.

3) Fit-ia the parts which are supplied separately alongwith the main machine.

4) See that there is no damage during transport, tighten the nut bolts, screws etc, if loose. 

5) Check the alignment of shaft, coupling etc, and tightness of terminal connections. 

6) Check the condition of bearings by moving the shaft manually and provide a lubrication/greasing. 

7) Check the clearance between stationary and rotating parts as per the

specifications.

8) Check the terminal connections and tighten them if required.

9) Bearings and lubrication for free and smoothness of rotating parts.

10) Check the spring tension, brush position and shape of brushes. commutator surface and commutator risers.

(B) Electrical Tests

1)Check winding resistance as per given value. 

2)Check insulation resistance between windings, between windings and core.

3) With external body.

4) Take reduced voltage run test. 

5)Check cooling systems of electrical operation.

6) Check earthing provision. After these primary tests the necessary ISI tests are carried out.

After these primary tests the necessary ISI test are carried out.

Different  Tests

The Indian Standard Institution (IS) has laid down the standard specifications for various machines and different tests are framed to check the standard and quality of the machine. These tests are generally grouped in four categories:

(a) Routine tests 

(b) Type tests

(c)Special tests 

(d) Supplementary tests.

(a)Routine tests : These tests are carried out on each and every machine manufactured in the industry.

(b) Type tests : These tests are carried out on few machines from the lot of the machines of same design and specifications. The test results of the few tested machines are treated same, for the complete lot of the machines. Say, if one hundred units are manufactured then random any 2 or 3 units are taken for testing.

(c)Special tests : These tests are carried out on machines for specified purpose only i.e. if a purchaser asks for results from these tests then only these are carried out and results are seen by the purchasers.

(d)Supplementary tests : These tests are performed whenever necessary and are not very common. These are carried out if additional information is required about a particular machine.

Routine tests, type tests are explained with neat circuit diagrams, observation tables, calculations and results etc in the respective chapters. In this chapter the test on D.C. Machines are explained.

Methods Of Testing

In order to check the performance such as efficiency, regulation, losses, change in condition of commutation, temperature rise, etc. the machines may be tested by direct  methods , indirect and regenerative methods.

1)Direct Method Of Testing

In this method the machine is directly connected with the load or a pulley and brake arrangement is provided or a electrical load may be connected in the form of a calibrated machine.

Brake test and calibrated machine test are the examples of direct tests. These are for rotating machine. For static machine like transformer load test is carried out by connecting electrical load on secondary.

2)Indirect Method Of Testing

As the name suggests load is not connected directly on the machine but it is run on no load and the data obtained from the no load test is used to find the efficiency, losses etc, at different loads.

Swinburne's test is the example of indirect test.

For transformer, O.C. and S.C. tests are the indirect tests. 

Advantages Of Indirect Testing

1. Facility to test high capacity machines on which direct loading not possible.
2. Time and energy saving in testing.
3. Results are approximate but not far away from actual.

3)Regenerative Method Of Testing

Two identical machines are electrically and mechanically connected together and output of second machine is fed back to first machine which saves power for testing. Hopkinson's test or Back to Back test is the example of regenerative test. 

Similar Back to Back test is carried on two identical transformers.

The above tests are explained in detail along with the illustrations below