Three-Phase Distribution Transformers - Siemens Sivacon S8 Planning Information

10.6 Three-phase distribution
transformers
Important parameters for the connection of the SIVACON
S8 low-voltage switchboard to three-phase distribution
transformers are listed in Tab. 10/6.
Approximation formulas for current estimation, if there are
no specified table values:
For the rated transformer current by approximation:
I = k x S
r rT
For the initial symmetrical transformer short-circuit current
by approximation:
I " = I / u
k r kr
Tab. 10/6: Rated currents and initial symmetrical short-circuit currents of three-phase distribution transformers
400 V AC / 50 Hz
Rated power
S
rT
Rated
current I
50 kVA 72 A
100 kVA
144 A
160 kVA 230 A
200 kVA 288 A
250 kVA 360 A
315 kVA 455 A
400 kVA 578 A
500 kVA 722 A
630 kVA 910 A
800 kVA 1,154 A
1,000 kVA 1,444 A
1,250 kVA 1,805 A
1,600 kVA 2,310 A
2,000 kVA 2,887 A
2,500 kVA 3,608 A
3,150 kVA 4,550 A
1) I
" uninfluenced initial symmetrical transformer short-circuit current in consideration of the voltage and correction factor of the transformer impedance in
k
accordance with IEC 60909-0, without considering the system source impedance
100 SIVACON S8 Planning Principles – Technical annex
Rated value of the short-
circuit voltage u
kr
4 % 6 %
Initial short-circuit
1)
alternating current I "
r k
1,933 A 1,306 A
3,871 A 2,612 A
6,209 A 4,192 A
7,749 A 5,239 A
9,716 A 6,552 A
12,247 A 8,259 A
15,506 A 10,492 A
19,438 A 13,078 A
24,503 A 16,193 A
- 20,992 A
- 26,224 A
- 32,791 A
- 41,857 A
- 52,511 A
- 65,547 A
- 82,656 A
Exemplified by
• Rated transformer power S
• Voltage factor k
k = 1.45 A/kVA for a rated voltage of 400 V
k = 1.1 A/kVA for a rated voltage of 525 V
k = 0.84 A/kVA for a rated voltage of 690 V
• Rated short-circuit voltage u
there are the following approximations for U
I
= (1.45 x 500) A = 725 A
r
I " = (725 x 100 / 4) A = 18.125 kA
k
Rated voltage
525 V AC / 50 Hz
Rated value of the short-
circuit voltage u
kr
4 % 6 %
Rated Initial short-circuit
current I alternating current I
r
55 A 1,473 A 995 A
110 A 2,950 A 1,990 A
176 A 4,731 A 3,194 A
220 A 5,904 A 3,992 A
275 A 7,402 A 4,992 A
346 A 9,331 A 6,292 A
440 A 11,814 A 7,994 A
550 A 14,810 A 9,964 A
693 A 18,669 A 12,338 A
880 A - 15,994 A
1,100 A - 19,980 A
1,375 A - 24,984 A
1,760 A - 31,891 A
2,200 A - 40,008 A
2,749 A - 49,941 A
3,470 A - 62,976 A
= 500 kVA
rT
=4 %
kr
r
690 V AC / 50 Hz
Rated value of the short-
circuit voltage u
4 %
Rated Initial short-circuit
1)
" current I alternating current I
k r
42 A 1,116 A
84 A 2,235 A
133 A 3,585 A
167 A 4,474 A
209 A 5,609 A
262 A 7,071 A
335 A 8,953 A
418 A 11,223 A
525 A 14,147 A
670 A -
836 A -
1,046 A -
1,330 A -
1,674 A -
2,090 A -
2,640 A -
= 400 V:
kr
6 %
1)
"
k
754 A
1,508 A
2,420 A
3,025 A
3,783 A
4,768 A
6,058 A
7,581 A
9,349 A
12,120 A
15,140 A
18,932 A
24,265 A
30,317 A
37,844 A
47,722 A