1. I, II and III type are basic models, suitable for various types of cable and bus bar entry.
2. V and C type are suitable for vertical bus bar entry.
3. M type is direct type, applicable to small current ratio with one turn for primary.
4. P type is simplified as protective type, as relay protection, also suitable for high precision measurement.
1.Type Explanation
Example: SD-0.66-40I-200/5A-5VA-0.5CL represents the product is used in power system up to 660V, 40mm copper bar entry through the window, rated burden is 5VA,
accurate class is 0.5%.
2.Technical Specification
SD-0.66 Series CTs are adapted to power system up to AC660V, 50/60Hz, as current measurement, energy measurement and relay protection. Working ambient
temperature is between -30℃ and +70℃,the highest temperature withstand is 120℃. The altitude above sea is ≤3000m, power frequency withstand voltage
is 3000V/1min.,50Hz, Insulation class is E, the CTs should be used in the condition that without direct attack from rain or snow, without serious pollution and
violent vibration.
3.Notice
3.1. Choose the matching window size of the CT according to the bus bar sizes and quantities,Other window size could be customized upon request.
3.2. Working voltage should not be higher than AC720V, and the working current should not be higher than 1.1 times of the rated current.
3.3. Choose the rated current and rated ratio according to load current, and normally 2/3 of the load current.
3.4. Polarity: P1,P2 for primary, S1,S2 for secondary.
3.5. Load impedance that the VA or Ω marked on the nameplate should not exceed the rated burden, and should not be left too much allowance.
3.6. When the installed meter is quite far from the CT or the loop impedance is quite big, 1A secondary outputCT should be considered as first choice.
3.7. Fixing torque of the wire connection screws:2.0～2.2N*m, fixing torque of the mounting screws:2.2～2.4N*m.
3.8. Open circuit of secondary circuit is not allowed in operation to avoid high voltage, if open circuit happens while in operation, demagnetization is required.
4.CTs’Selection Guide
Electro-technical measuring and metering instrument proper configuration with：
4.1.Regulated by Standards GB20840《Instrument Transformer》,The standard values of rated secondary currents are 1 A, 2 A and 5 A, but the preferred value is 5A.
when transmission distance is much longer, 1A and 5A have more advantages.
4.2.Decrease the line power consumption: The line power consumption is in proportion to the square of current, the power consumption of 1A secondary output CT will
decrease 25 times than 5A’s, that means 1A’s power consumption is only 4% of 5A’s. When designing a 1A system, the instrument’s resistance is only considered
(ignore the contact resistance).
Measuring line power consumption (VA) Table 1
|
Wire section (mm2) |
Secondary current (A) |
Transmission distance (m) One-way round trip |
||||
|
1 |
2 |
5 |
8 |
10 |
||
|
1.5 |
1 |
0.023 |
0.048 |
0.117 |
0.187 |
0.234 |
|
5 |
0.58 |
1.17 |
2.93 |
4.68 |
5.58 |
|
|
2.5 |
1 |
0.014 |
0.028 |
0.07 |
0.112 |
0.14 |
|
5 |
0.35 |
0.70 |
1.76 |
2.81 |
3.51 |
|
|
4 |
1 |
0.009 |
0.018 |
0.044 |
0.070 |
0.088 |
|
5 |
0.22 |
0.44 |
1.1 |
1.76 |
2.19 |
|
● Enlarge the transmission distance: Per the secondary load calculation formula of the CT S=I2Z, given the same load, the transmission distance of 1A CT is 25 times of 5A
CT’s, so can avoid to select 5/1A CT or big capacity CT.
Transmission distance of different rated burden (m) Table 2
|
Rated burden（VA） |
Ampere rating（A）
|
Wire section（mm2） |
|||
|
1 |
1.5 |
2.5 |
4 |
||
|
2.5 |
1 |
69 |
108 |
178 |
277 |
|
5 |
2.8 |
4.3 |
7.1 |
11.1 |
|
|
5 |
1 |
138 |
216 |
356 |
554 |
|
5 |
5.5 |
8.6 |
14 |
22.2 |
|
|
10 |
1 |
276 |
432 |
712 |
1108 |
|
5 |
11 |
17 |
28.5 |
44.3 |
|
● Decrease the wire section: at large and medium-sized enterprises, when the instrument and the CT are far from each other (e.g. 80m), from table 4, when select 5A, 10VA
CT, the wire section needs 8mm2 by the calculation. If select 1A, 2,5VA, only 1.5mm2 wire is required. Currently with the popularization and development of computer and
numerical controlled instrument, 1A and below rating CT is very popular.
4.3 There is feedback sometimes from field commissioning that the ammeter value is much different with the actual. The root cause is the secondary burden is bigger that the
rated. The secondary burden includes three parts: a) Measuring and metering meter’s power consumption(table 3); b) The secondary wire’s power consumption(table 1);
c) The secondary contact resistance(0.15～0.1Ω). Should calculate secondary burden firstly when designing, then confirm CT’s rated burden.
Power consumption of common instruments (reference) Table 3
|
Instument |
Instrument type |
Each current coil |
|||
|
Power consumption（VA） |
Resistance（Ω） |
Quantity |
|||
|
Ammeter |
Rectified |
42L,6L,63L,45L |
0.2-0.4 |
|
1 |
|
Electromagnetic |
1T1,1T9 |
3 |
0.12 |
1 |
|
|
Power meter |
Rectified |
42L,6L,63L,45L |
0.3-0.6 |
|
1/2/3 |
|
Electric |
1D1,16TD3 |
1.5 |
0.06 |
||
|
Power factor meter |
Rectified |
42L,6L,63L,45L |
0.4-0.8 |
|
1 |
|
Electric |
1D1 |
3.5 |
0.14 |
1 |
|
|
Watt-hour meter |
Single phase |
DD8 |
1-2 |
|
1 |
|
Three-phase three-wire |
DS1,DS2,DS8,DX1,DX2,DX8 |
0.5 |
0.02 |
2 |
|
|
Three-phase four-wire |
DT1,DT2,DT8,DX1,DX2,DX8 |
1.5 |
0.06 |
3 |
|
|
Electrical transmitter |
|
SL,CD |
0.3（1） |
（non-current） |
|
|
|
FP,UFP（0.2CL） |
<0.2 |
|
|
|
|
|
|||||
|
|
GP,UFP（0.5CL） |
<0.5 |
|
|
|
|
|
BD |
≤0.3 |
|
|
|
|
Multifunction meter |
|
ACR |
<0.2 |
<0.1 |
|
|
|
PM800（Schneider） |
<0.15 |
<0.1 |
|
|
Relay’s power consumption Table 4
|
Relay |
Relay’s type |
Each current coil |
||
|
Power consumption（VA） |
Resistance（Ω） |
Remark |
||
|
Current relay
|
DL-¨/0.01-0.05 |
0.08（0.4） |
0.004 |
DL-10(20C/300) and DD-11(1) the power consumption is the power that consumed at the first current setting or at the minimum setting value, the maximum value is 2.5 times of the listed while not 4 times. GL-10/20(LL-10) the power consumption means the maximum ( in parallel / in series)
|
|
DL-¨/0.2-6 |
0.1（0.55） |
0.004 |
||
|
DL-¨/10-15 |
0.15（0.8） |
0.006 |
||
|
DL-¨/20 |
0.25（1.0） |
0.01 |
||
|
DL-¨/50 |
1.0（6/2.8） |
0.04 |
||
|
DL-¨/100 |
2.5（20/7.5） |
0.1 |
||
|
DL-¨/200 |
10（32） |
|
||
|
DL-¨/5-10 |
15（10） |
|
||
|
Grounding relay |
DL-¨/40 |
0.012 |
80/20 |
|
|
DL-¨/50 |
52/13 |
|||
|
DL-¨/60 |
36/9 |
|||
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