I.B. 17555C
Effective November 1999
Page B9
6.3
CT SATURATION
The DSPS has been designed and extensively tested to
assure continued relay powering when the main cts satu-
rate. It powers the relay even for extreme cases in which
the ct delivers only a succession of current spikes of 1 to
2 ms each half-cycle.
But pay attention to the standard measuring limitations of
any protective relay with saturated cts.
The saturated ct is
exhibiting serious ratio error, and any connected relay will
measure lower current than is actually flowing in the pri-
mary circuit. Tripping times will be longer than planned. In
extreme cases, the relay may not trip at all.
The Digitrip 3000 is a true RMS measuring device, and
will integrate the spikes and dead periods to arrive at a
current measurement. The user should follow standard
application guidelines of comparing the ct saturation
curve with the total connected burden, in light of the max-
imum fault current. The total burden includes all con-
nected measuring device current windings, plus
resistance of the ct secondary winding itself and all inter-
connecting wiring. Since saturation curves are plotted
with RMS-measuring instruments, measurement errors
and tripping times can be predicted with good reliability.
The Digitrip 3000 with DSPS can help to reduce ct satu-
ration problems. The current-powering transformers have
been designed to present lower burden than most “self-
powered” relays, especially for large fault current magni-
tudes. The burden is much lower than that of an electro-
mechanical relay.
6.4
BURDEN DATA
In normal operating conditions, the burden is <0.08 ohms
with 3-phase 1A ct current, or 0.2 per unit, and drops to
less than 0.04 ohms at high current levels. Figures B-7
and B-8 present ct burden data in ohms and volt-
amperes. In these cases, the burden shown is the total ct
terminal value, which is the DSPS plus the relay measur-
ing circuits, for the indicated operating condition.
Figure B-7 shows burden impedance magnitude in ohms.
The two lower curves are the values with ac power
applied; the upper two are with ct powering only. For each
of these pairs, one curve shows the burden for a single-
phase current (representing a single-phase-to-ground
fault) and the other for three balanced phases with nor-
mally arrayed 120-degree phase angle increments. There
is no phase sequence sensitivity.
Figure B-8 shows the burden in volt-amperes for the
same four cases.
The three-phase burden cases assume the normal angu-
lar distribution of the phases at 120-degree intervals. If
the three-phase current inputs are connected in series to
a single current source for a lab-bench test, burden
results will be slightly different.
Содержание Cutler-Hammer Digitrip 3000
Страница 18: ...I B 17555C Effective November 1999 Page 12 Fig 2 1 Typical Communications Wiring Diagram...
Страница 27: ...I B 17555C Effective November 1999 Page 21 Fig 3 1 Digitrip 3000 Typical Wiring Diagram...
Страница 36: ...I B 17555C Effective November 1999 Page 30 Fig 3 11 Local Programming Sequence Flow Chart...
Страница 37: ...I B 17555C Effective November 1999 Page 31...
Страница 48: ...I B 17555C Effective November 1999 Page 42 Fig 7 1 Inverse Time Overcurrent Phase I4T Curves SC 5390 92B...
Страница 49: ...I B 17555C Effective November 1999 Page 43 Fig 7 2 Inverse Time Overcurrent Phase I2T Curves SC 5391 92B...
Страница 50: ...I B 17555C Effective November 1999 Page 44 Fig 7 3 Inverse Time Overcurrent Phase IT Curves SC 5392 92B...
Страница 51: ...I B 17555C Effective November 1999 Page 45 Fig 7 4 Inverse Time Overcurrent Phase Flat Curves SC 5393 92B...
Страница 52: ...I B 17555C Effective November 1999 Page 46 Fig 7 5 Short Delay Phase Curves SC 5394 92B...
Страница 53: ...I B 17555C Effective November 1999 Page 47 Fig 7 6 Inverse Time Overcurrent Short Delay Curves SC 5395 92B...
Страница 54: ...I B 17555C Effective November 1999 Page 48 Fig 7 7 Instantaneous Curves SC 5396 92B...
Страница 55: ...I B 17555C Effective November 1999 Page 49 Fig 7 8 Inverse Time Overcurrent Ground I4T Curves SC 5399 92B...
Страница 56: ...I B 17555C Effective November 1999 Page 50 Fig 7 9 Inverse Time Overcurrent Ground I2T Curves SC 5400 92B...
Страница 57: ...I B 17555C Effective November 1999 Page 51 Fig 7 10 Inverse Time Overcurrent Ground IT Curves SC 5401 92B...
Страница 58: ...I B 17555C Effective November 1999 Page 52 Fig 7 11 Inverse Time Overcurrent Ground Flat Curves SC 5402 92B...
Страница 59: ...I B 17555C Effective November 1999 Page 53 Fig 7 12 Short Delay Ground Curves SC 5403 92B...
Страница 60: ...I B 17555C Effective November 1999 Page 54 Fig 7 13 ANSI Moderately Inverse Curves SC 6685 96...
Страница 61: ...I B 17555C Effective November 1999 Page 55 Fig 7 14 ANSI Very Inverse Curves SC 6686 96...
Страница 62: ...I B 17555C Effective November 1999 Page 56 Fig 7 15 ANSI Extremely Inverse Curves SC 6687 96...
Страница 63: ...I B 17555C Effective November 1999 Page 57 Fig 7 16 IEC A Moderately Inverse Curves SC 6688 96...
Страница 64: ...I B 17555C Effective November 1999 Page 58 Fig 7 17 IEC B Very Inverse Curves SC 6689 96...
Страница 65: ...I B 17555C Effective November 1999 Page 59 Fig 7 18 IEC C Extremely Inverse Curves SC 6690 96...
Страница 66: ...I B 17555C Effective November 1999 Page 60 Fig 7 19 IEC D Flat Curves SC 6691 96...
Страница 68: ...I B 17555C Effective November 1999 Page 62...
Страница 73: ...I B 17555C Effective November 1999 Page A5 Fig A 7 DT3001 Typical Wiring Diagram...
Страница 76: ...I B 17555C Effective November 1999 Page A8...
Страница 81: ...I B 17555C Effective November 1999 Page B5 Fig B 2 Digitrip 3010 3020 Dimensions Inches...
Страница 83: ...I B 17555C Effective November 1999 Page B7 Fig B 3 Digitrip 3010 3020 Typical Wiring Diagram...
Страница 89: ...I B 17555C Effective November 1999 Page B13...
Страница 90: ...I B 17555C Effective November 1999 Page B14...
Страница 91: ...I B 17555C Effective November 1999 Page B15...