IEC 61869-1 classifies instrument transformer tests as type, routine, special and sample tests, and lists them in its Table 10. Each product part (current, inductive voltage, combined and capacitor voltage) replaces that table with the tests specific to the equipment. Type tests are performed on a maximum of two units and routine tests on every unit manufactured.
Short answer
An instrument transformer goes through four kinds of tests. Type tests demonstrate the design. Routine tests are performed on every unit that leaves the factory. Special tests are performed only if purchaser and manufacturer agree. Sample tests are performed on a few units of a batch. Table 10 of IEC 61869-1 lists the tests, and each product part (current, voltage, combined and capacitor) replaces it with the list for that equipment.
The four classes of tests
Clause 7.1.1 of IEC 61869-1 (2007 edition) defines each class:
- Type test. Performed on one unit to demonstrate that all units made to the same specification meet the requirements that routine tests do not cover.
- Routine test. Performed on every unit. Its purpose is to reveal manufacturing defects, and it does not damage the properties or reliability of the unit.
- Special test. A test other than a type or routine test, agreed between manufacturer and purchaser.
- Sample test. A type or special test performed on one or more complete units from a defined production batch.
Type tests have general rules (clause 7.2.1). All dielectric type tests are performed on the same transformer, unless stated otherwise. Type tests are performed on a maximum of two units, at an ambient temperature between 10 °C and 30 °C. A minor design deviation does not invalidate the test, provided manufacturer and purchaser agree to it.
The base list in part 1
Table 10 of IEC 61869-1 groups the tests as follows:
| Class | Tests |
|---|---|
| Type | Temperature rise; lightning impulse on primary terminals; wet test for outdoor equipment; electromagnetic compatibility; accuracy; enclosure degree of protection; enclosure tightness and pressure test |
| Routine | Power-frequency voltage on primary terminals; partial discharge; between-section voltage; power-frequency voltage on secondary terminals; accuracy; verification of markings; enclosure tightness and pressure |
| Special | Chopped impulse and multiple chopped impulses; capacitance and dissipation factor; transferred overvoltage; mechanical tests; internal arc; tightness at low and high temperature; gas dew point; corrosion; fire hazard |
| Sample | Defined in annex D |
If the transformer uses gas insulation, Table 11 sets the gas type and the pressure for each test. Almost all are performed with the same service fluid. The exception is the transferred overvoltage test, which is performed at reduced pressure and does not require the service gas.
What changes in each product part
Each part replaces Table 10 and adds its own tests.
| Part | Equipment | Tests it adds |
|---|---|---|
| IEC 61869-2 | Current transformer | Type: short-time currents. Routine: secondary winding resistance, secondary loop time constant, knee-point emf and excitation current, and inter-turn overvoltage. Sample: remanence factor and instrument security factor (FS) of the measuring CT |
| IEC 61869-3 | Inductive voltage transformer | Type: short-circuit withstand capability. Electromagnetic immunity does not apply |
| IEC 61869-4 | Combined transformer | Adds up the CT and VT lists |
| IEC 61869-5 | Capacitor voltage transformer | Type: capacitance and tan δ, short-circuit, ferroresonance, transient response for protective classes, and carrier-frequency accessories. Routine: ferroresonance check and accessories. Special: temperature coefficient and tightness of the capacitor units |
In the CT, secondary resistance, time constant, knee point and the inter-turn test are routine tests: they are performed on every unit, not only on the design.
The order in which they are performed
Clause 7.1.3 sets the sequence. After the dielectric type tests, the same transformer goes through all the routine tests. Special tests can alter that sequence.
- Dielectric type tests. On the same transformer
- All routine tests. Those of clause 7.3, on that transformer
- Agreed special tests. May influence the sequence above
For the capacitor transformer, IEC 61869-5 replaces clause 7.1.3 with a sequence diagram that is mandatory. A small change to that order requires agreement between manufacturer and purchaser.
How to use the list on a project
- At purchase. Request the type test report for the design and the list of routine tests for each unit. If you need a special test, write it into the specification.
- At receiving. Compare the report against the list for the part that applies to your equipment. A CT without secondary resistance or knee point, or a CVT without a ferroresonance check, is incomplete.
- At commissioning. Field tests do not replace factory tests. They confirm that the unit did not change in transport and that its wiring is correct.
What not to do
- Do not accept a type test report for a design different from the one you are buying, without a written agreement on the differences.
- Do not assume special tests were performed. They are requested.
- Do not use a field test as a substitute for a factory routine test.
- Do not mix the list of one part with another: a CVT does not follow the list of the inductive voltage transformer.
Related topics
Routine and type tests include power-frequency withstand and induced voltage, partial discharge, impulse tests and inter-turn overvoltage. On site they are grouped under primary equipment testing, following the standards for primary equipment tests. See also current transformers and CVT.
When to contact us
At Tiza Group we review factory test reports against the standard and perform field tests on instrument transformers. See our testing and commissioning service, available in Colombia, or elsewhere on request. Write to us and we will send you a quote.
Related guides
- Applied and induced voltage in a voltage transformer
- Partial discharge in instrument transformers
- Impulse tests on instrument transformers
- Substation primary equipment testing: guide by equipment
- Standards for substation primary equipment testing
References
- IEC 61869-1, Instrument transformers - Part 1: General requirements, 2007 edition: clauses 7.1.1 to 7.1.3, 7.2.1, 7.5, Table 10, Table 11 and annex D.
- IEC 61869-2, 2012 edition: Table 10, clauses 7.2.201, 7.3.201 to 7.3.204 and 7.5.
- IEC 61869-3, 2011 edition: Table 10 and clause 7.2.301.
- IEC 61869-4, 2013 edition: Table 10.
- IEC 61869-5, 2011 edition with the 2015 correction: Table 10 and clause 7.1.3.
Frequently asked questions
What is the difference between a type test and a routine test?
A type test is performed on one unit to demonstrate that all units made to the same specification meet the requirements that routine tests do not cover. A routine test is performed on every unit and serves to reveal manufacturing defects without damaging its properties or reliability.
Is a special test mandatory?
Not by itself. IEC 61869-1 defines it as a test other than a type or routine test, performed by agreement between manufacturer and purchaser. If you need it, you must request it at purchase.
What additional tests does a capacitor voltage transformer have?
IEC 61869-5 adds, among the type tests, capacitance and tan δ measurement, short-circuit withstand, ferroresonance, transient response (for protective classes) and tests of the carrier-frequency accessories. Among the routine tests it adds the ferroresonance check and the routine tests of the accessories.