On a transformer name plate %IZ(%Impedence) is mentioned.
What is the meaning of %IZ and how it is calculated?
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
Any Electrical Engineering jobs?Please refer for interviews. Thank you
Please tell me the power flow from pmg to main rotor of an alternator (Including AVR unit)?
Why water bubbles when D.C. Current is passed through it? Why not when A.C. Current is passed?
What do you mean by ratio correction factor of instrument transformer?
why the rotor current becomes in steady state during high slip region? please verify with equations.
How to calculate the phase to phase clearness of HT /// LT bus bar?????
EXPLAIN USE OF ROCKING ARRANGEMENT IN ELECTRIC HEATING?
why power factor is important?
Why is negative feedback invariably preferred in closed loop system?
why we used dc supply for field in dg set
What are the advantages of speed control using thyristor?
How do we calculate over and under frequency tolerance from generator data?
My question is whether bellow formula is correct to find bus size for 46kA for 0.5 second & what is RT in bellow formula. formula to calculate the size of busbar to withstand the thermal stresses due to currents with duration of 0.2 sec to 5 sec. Sp = RT( I x I x t) / K Where Sp – is the cross sectional area of bus bar in millimeters. I - is the value of AC fault current. t - is the operating time of disconnecting device in seconds. K – is the factor depending on the material of the conductor, insulation and initial and final temperature. Value of ‘k’ for copper is 143.
WHAT IS DIFFERENCE BETWEEN CAPACITOR AND CAPACITANCE?
How to calculate or formula to calculate rhe power in 2 phase system ??