On a transformer name plate %IZ(%Impedence) is mentioned.
What is the meaning of %IZ and how it is calculated?
- 3 Answers
- 25555 Views
- Ambe Consultancy, Siemens, I also Faced
- E-Mail Answers
Answer Posted / bhaskar goswami
Calculating the Short Circuit Current when there is a Transformer in the circuit. Every transformer has “ %” impedance value stamped on the nameplate. Why is it stamped? It is stamped because it is a tested value after the transformer has been manufactured. The test is as follows: A voltmeter is connected to the primary of the transformer and the secondary 3-Phase windings are bolted together with an ampere meter to read the value
of current flowing in the 3-Phase bolted fault on the secondary. The voltage is brought up in steps until the secondary full load current is reached on the ampere meter connected on the transformer secondary.
So what does this mean for a 1000KVA 13.8KV – 480Y/277V.
First you will need to know the transformer Full Load Amps
Full Load Ampere = KVA / 1.73 x L-L KV
FLA = 1000 / 1.732 x 0.48
FLA = 1,202.85
The 1000KVA 480V secondary full load ampere is 1,202A.
When the secondary ampere meter reads 1,202A and the primary Voltage Meter reads 793.5V. The percent of impedance value is 793.5 / 13800 = 0.0575. Therefore;
% Z = 0.0575 x 100 = 5.75%
Taken From:
Simple Methods for Calculating Short Circuit Current
Without a Computer
By Dennis McKeown, PE
GE Senior System Application Engineer
| Is This Answer Correct ? | 4 Yes | 0 No |
Post New Answer View All Answers
What are the application of filter?
1) Explain why we don't link the two earthing system ht and mv on a pole mounted transformer sub-station.
why high speed tripping relay will be used in tripping circuit why not normal relay
Explain marx circuit.
What is the effect on 3phase induction motor if current setting knob of DOL kept at minimum current?
what is the AC Plant and how can do the work with parts and picture tell us 150 Tr
What are unstable systems?
What is different between resistance grounding system and resistance earthing system?
What is the direction of current flow in ct secondary...means if the current is flowing from P1 to P2 then what will be the direction of current flow in ct secondaryw
True or false question. 1.The fuse provide phase and neutral 2.power loss in electrical circuit can take place in (resistance or inductance or capacitance). 3.two phase system each phase has separated by a phase difference of (90 or 180 or 270 or 45). 4.3 phase balanced star connected load neutral current shall be (line current or phase current or zero or unity)
Why does the Solid state Rectifiers for 3-ph brake motors sometimes have 2 & sometimes 3 output terminals?
What is the Basic Difference bitween Long Shunt Connection and Short Shunt Connection in DC Generator?
If not into production, how far did you follow the design and why did not you see it into production?
How to calculate the electrical load for a standard telecom BTS shelter and choose the DG set capacity for the same load?
what is laser diodes?
