ELCOME dear friends of protection and control engineering. How many of the following questions about current transformers can you answer right off the bat? You can find the solutions at the end of the article, here we go:
Question 1
What are low voltage CT's called?
a) combined c.t.
b) window type c.t.
c) voltage transformer
Question 2
The transfer of the primary current to the secondary side is not ideal. Decisive for the transfer is:
a) the linear characteristic of the transformer
b) the size of the transformer
c) the main inductance
Question 3
The remanent flux (Ψr) is that value of flux which would remain in the core:
a) 50 min
b) 5 min
c) 3 min
d) 10 min
after the interruption of an exciting current of sufficient magnitude to induce the saturation flux (Ψs).
Question 4
Uniformly aligned domains are responsible for the residual magnetization of ferromagnetic materials. These are called as follows:
a) Bloch-walls
b) Molecular magnets
c) Weiss domain
d) Magnet domain
Question 5
Older current transformers often still have old terminal designations. What was the name of the primary terminals in the past?
a) H & M
b) P & R
c) k & l
d) K & L
Question 6
The "simplified equivalent circuit diagram" of a current transformer looks as follows (see figure). The parallel branch of the main inductance inductance and the:
a) primary current
b) magnetizing current
c) secondary current
d) reactive current
resulting from it, are the main cause of the overall error of a current transformer.
Question 7
When the primary current flows from P1 to P2, it must always flow out at the:
a) secondary terminal S1.
b) secondary terminal S2.
c) grounding terminal.
Question 8
It follows from Lenz's rule that the secondary current and the magnetic field resulting from it:
a) amplify the magnetic flux of the iron core.
b) counteract the magnetic flux of the iron core.
c) are aligned with the magnetic flux of the iron core.
Question 9
The Holmgreen circuit is very well suited for use in connection with
a) transient earth fault relays
b) distance protection relay
c) wattmetric eath fault relay
Question 10
If the number of turns on the primary side is reduced:
a) the secondary current drops.
b) the secondary current increases.
c) the secondary current remains the same.
Thank you very much
Your EEA-Team
The proper answers are:
1. b
2. c
3. c
4. c
5. d
6. b
7. a
8. b
9. a
10. a
