LOW VOLTAGE CURRENT TRANSFORMER LOW VOLTAGE CURRENT TRANSFORMER

GENERAL BURDEN Cable length: RL is proportional to the length of cabling the assigned current when it is connected to its nominal load, Sc

Current Transformer (C.T.) is used to transform the high A C current (there and back) (V·A)=Zc·(/sn) 2 According to Standards, for apparent power
Ranging from 1.5-30VA
to small easily manageable values. They're connected with the P anel greater than or equal to 5VA, the power factor is 0.8 inductive. For

Meter or Relay and thery can help to measure the current or protect RATED SECONDARY CURRENT Power: apparent power less then 5V·A the power factor is considered to be
the equipments. Low voltage current transformers are manufactured The nominal apparent power(V A) with a specified power factor, which one(unity).
x/5A (x/1A upon request)
as of two tyees for measuring CT and protection CT. was supplied by the Current Transformer, to the secondary current with

RATED PRIMARY CURRENT

MEASURING CT
Ranging up to 6000A
Measuring current transformers are constructed to feed on other low ACCURACY OF A CURRENT TRANSFORMER
voltage apparatus such as measuring instruments, relays, watt-hour INSULATION The percentage of error, produced in a transformer, is established by
V·A
meters (kW meter) and these type of current transformers are mainly used Class B for Casing type CT V·A
5 IEC60044-1. In measurement transformers: 25 % and 100 % of nominal
0.5 and 1 class to transfer the current from highest rated current to rated Class A for Taping type CT
secondary current.
.../5A power. In protection transformers: 100 % of nominal power.
4
CASING

.5m 2
m

m2
PROTECTION CT 3

.5m
Non-flammable, polycarbonate self extinguishing ABS/PC

2
s=1

m
2

4m
2

s=
m

s=
6m
Protection current transformers are constructed to feed the protection 2 s=
m
2

10m
relay. These type of current transformers are mainly used 5P. (Customer TERMINAL MARKS s=

supplied when required.) VO to UL94 1

Primary P1 & P2(K & L)
Secondary SI & S2(K & L) 5 10 15 20 25 30 35 40 45 50 (m) Note: With.../1A transformers losses are reduced 25 times
REFERENCE STANDARDS Length of secondary line
IEC60044-1, VDE0414-44-1, DIN57414, BS3938, Bs7626, SELECTION OF THE CURRENT TRANSFORMER
EN60044-1, GB1208-2009
To select the Current Transformer correctly, the following points should
be clarified: ERROR LIMITS. ACCURACY CLASSES OF MEASURING CT
SECURITY FACTOR
The application(for measuring or protection)
FS<5 ±﹪Error for﹪1 n Phase Difference ±for﹪1 n
The features of the wording environment(indoor or outdoor, operating
Accuracy
MAXIMUM SYSTEM VOLTGE temperature, air humidity etc...) Minutes Centiradians
Classes
Operation voltage and frequency 5 20 100 120
5 20 100 120 5 20 100 120
720V AC
Range of the primary current(maximum and minimum of the current
0,1 0.40 0.20 0.10 0.10 15 8 5 5 0.45 0.24 0.15 0.15
TEST VOLTAGE to be measured)
0,2 0.75 0.35 0.20 0.20 30 15 10 10 0.9 0.45 0.30 0.30
3kV AC(1 min.) Dimension of the cable or bus bar
Data of the overload 0,5 1.50 0.75 0.50 0.50 90 45 30 30 2.7 1.35 0.90 0.90
FREQUENCY Short circuit current 1,0 3.00 1.50 1.00 1.00 180 90 60 60 5.4 2.70 1.80 1.80
50/60Hz Specification of the measuring device associated with the Current
Transformer(accuracy, rated current, consumption ect...)
RATED SHORT-TIME THERMAL CURRENT
The diameter and length of the cable. the cable which is used to
Ith=60 X In Phase Difference ±for﹪1 n
connect the Current Transformer and associated measuring device ±﹪Error for﹪1 n
Ith limited by cable sizes or primary bus-bar for other case Accuracy
Minutes Centiradians
Classes
1 5 20 100 120
RATED DYNAMIC CURRENT 1 5 20 100 120 1 5 20 100 120
POWER LOSSES OF THE CT
0,2S 0.75 0.35 0.20 0.20 0.20 30 15 10 10 10 0.90 0.45 0.30 0.30 0.30
Idyn=2.5 X Ith In the practial application, the power generated by the primary
0,5S 1.50 0.75 0.50 0.50 0.50 90 45 30 30 30 2.70 1.35 0.90 0.90 0.90
current should be equal or bigger than the power requirement of
CONTINUOUS OVERLOAD
the associated measuring device plus the consumption of the connecting
1.2 X In
Line.

OPERATING TEMPERATURE Accuracy

Losses in the line, PL; ±﹪Error for﹪1 n
Classes
-25℃～+50℃ This is the power lost, through heat, generated by current through the
resistance RL in the cables, in the transformer's secondary circuit. % ln 50 120
ACCURACY
3 3 3
Measuring 0.5; 1.0; 3.0(special accuracy upon request) Factors to be taken into account: 5 5 5
Protection 5P; 10P Secondary current: PL=RL/2

Cable diameter: RL is inversely proportional to the square of the diameter

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 LOW VOLTAGE CURRENT TRANSFORMER LOW VOLTAGE CURRENT TRANSFORMER

ERROR LIMITS. ACCURACY CLASSES OF PROTECTION CT

DEMO
Accuracy Phase Difference ±for﹪1 n Composite
Classes ±﹪Error for﹪1 n Error
Minutes Centiradians

5P ±1 ±60 ±1.8 5

10P ±3 -- -- 10

SATURATED CONDITION OF CT
The current transformer is saturated if the primary current, on the secondary side, protection CT will not saturate until there
2T 100/5A 1T 50/5A
passing through the CT, is greater than the nominal rating is a very high current on the primary side. A Class 5P15 protection
of the CT. transformer indicates that it has an accuracy rating of 1% that
The linearity of CT, between the primary and secondary it does not become saturated until the primary current reaches CONSTRUCTION
sides decreases, so error increases. The saturation of the CT 15 times the nominal current rating of the CT.
CT consist of primary winding, secondary winding, magnetic core and tape wound ring type current transformer, the PEW coated windings are then
is inversely proportional to the load (Fig. 1). I n m e a s u r i n g t r a n s f o r m e r s , t h e S A F E T Y FAC T O R " F S " p a r a m e t e r
insulated body. The high-grade silicon steel core is annealed, varnished covered with elephantite paper, varnished and double-tapped with PVS tapes.
The d i f f ere n c e b e t w e e n measuring and protection current indicates the excessive amperage on the primary side current in
then insulated with polycarbonate core caps. The secondary winding is For the encapsulated type current transformer, the windings are enclosed in a
transformers is their behavior when an overload occurs on relation to the current sent to the measuring device on the toroidally wound by high precision semi-automatic machinery. For the compact and heat resistant split cap.
the primary side. Measuring CT is saturated when there is secondary side
a p r i m a r y c u r r e n t o v e r l o ad. In order to protect the equipme n t , Iron Core annealed and varnished

FIG.1

CLASS CURVES A: Rated Current Zone. The secondary terminals (depends on models)
B B: Overcurrent zone for protectiong CT.
C: Max. Overcurrent zone for measuring CT.
Polycarbonate core split cap
A C
The Secondary winding (100% copper)
%
1.2 5 x lpn
0
1
Current Error

3
Protection CT
Measuring CT
0.5 10P5 5P5

Instrument Burden Consumed

Moving iron instruments 0.3-15VA A. Permalloys Core B. Silicon Core
Moving coil instruments 0.5VA
Analogue power meter 0.2-2.5VA KIND REMINDER:
Maximum Demand Ammeter 2.5-5.0VA Improper selection, installation or operation can cause danger to personal security!
Digital Meter
! Don't open the secondary circuit when the current is available in the primary circuit. Or it will cause high voltage which is dangerous to
0.5-1.0VA
personal security!
Energy Meter 1.0-1.5VA
Resistance of current transformer is very low, so that secondary winding of current transformer can be operated as a shortcircuit, when
Recording Instruments 2.0-5.0VA required in test operation. Otherwise, this condition causes high voltage and can be dangerous during usage.
When selecting a current transformer, it is important to consider the power absorbed by the cables connected betweent the CT secondary
terminals and the measuring instrument. The resultant cable burden should be added to the equipment burden, and the total should not exceed
APPLICATION NOTE the available VA of the CT.
P1 (K) must face the supply feeder, and P2(L) must face the load. It is also important to ensure that secondary connections are made in accordance
If the primary current is too small, to keep the same accuracy and output, Transformer with the primary current be turned twice which help to keep with instrument diagrams. The secondary terminals of the CT must NOT be open-circuited on load as dangerously high voltages may be present
we can add primary winding, but the rated turns ratio should be the same. the samerated turns ratio(1:50 = 2:100). under these conditions. It is recommended that one side of the secondary windings is earthed.

For example, if the primary current is 50A, we can use 100/5A Current

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 LOW VOLTAGE CURRENT TRANSFORMER LOW VOLTAGE CURRENT TRANSFORMER

FEATURE MSQ Series Burden(VA)

Ratio Case Item
(A) Qty.(Pcs) Code
Class:0.5 Class:1.0
ATO-CT-800
30/5 1.5 1.5 60 104001005
11.5 150/5 1.5 2.5 60 104001505

φ31 200/5 2.5 5 60 104002005

11.5

42
21.5
16.5
250/5 5 5 60 104002505

Built In Hinged Sealable Terminal Cover 300/5 5 5 60 104003005

11.5
( Metallic sealable screw for option) Busbar Suppout Mounting 22.2 400/5 5 10 60 104004005
35.4
42
800/5 5 10 60 104005005
Note: Class/VA rating must be mentioned when ordering.

98

71

43
60
Casing Self-extinguishing Class VO Panel Mounting( through plastic fixing kit )
74.5

ATO-CT-1000
Ratio Burden(VA) Case Item
(A) Qty.(Pcs) Code 200/5
Class:0.5 Class:1.0 1.5 2.5 32 106002505
ATO-CT-075 5/5 5 7.5 36 130100055 250/5 2.5 5 32 106003005
V
D E
10/5 5 7.5 36 130100105 φ46 300/5 5 10 32 106004005

15/5 5 7.5 36 130100155 500/5 5 10 32 106005005

21
51
23
B+0.24+0.10

31.5

20/5 5 7.5 36 130100205 600/5 5 10 32 106006005

D

11

+0.28 25/5 5 7.5 36 130100255 52

61
750/5 5 10 32 106007505
C 0

30/5 5 7.5 36 130100305 800/5 7.5 10 32 106008005

40/5 5 7.5 36 130100505 1000/5 10 15 32 106010005

50/5 5 7.5 36 130100605 / 10 15 32 106012005

/

127
75/5 5 7.5 36 130101005 15 15 32 106015005

73

45
62
/ 5 7.5 36 130101505 / 15 15 32 106016005
104

118

55
86

/ 5 7.5 36 130102005 Note: Class/VA rating must be mentioned when ordering.

103
/ 5 7.5 36 130102505
87 / 5 7.5 36 130103005
Note: Class/VA rating must be mentioned when ordering. 300/5 5 10 12 108507505
ATO-CT-400 ATO-CT-1500
400/5 5 10 12 108508005
30/5 - 1.5 (3T) 60 103000305
500/5 7.5 10 12 108510005
50/5 - 1.5 (2T) 60 103000405
φ24 φ82 600/5 10 15 12 108512005
75/5 - 2.5 (2T) 60 103000505
750/5 10 15 12 108515005
31.5
21.5
11.5

82.5

11
86

32
100/5 - 2.5 (2T) 60 103000605
1200/5 10 15 12 108516005
11.5 150/5 - 1.5 60 103000755
21.5
11
32
1500/5 15 15 12 108520005
31.5 200/5 - 1.5 60 103000805 82.6
86

- Note: Class/VA rating must be mentioned when ordering.

250/5 2.5 60 103001005

300/5 - 3.75 60 103001505

400/5 5 5 60 103002005
98

/ 5
164
71

43
60

7.5 60 103002505
42
67
57

/ 10 10 60 103003005

74.5 Note: Class/VA rating must be mentioned when ordering.

128

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 LOW VOLTAGE CURRENT TRANSFORMER

Ratio Burden(VA) Case Item

(A) Qty.(Pcs) Code
Class:0.5 Class:1.0

ATO Current Transformer

500/5 5 5 16 110008005
ATO-CT-2500
600/5 10 10 16 110010005

φ62.5
750/5 10 15 16 110012005
800/5 10 15 16 110012505
10.5
32

1000/5 10 15 16 110015005
61.5
81 1200/5 10 15 16 110016005
101

1500/5 10 15 16 110020005
2500/5 10 15 16 110025005
3000/5 10 15 16 110030005

Note: Class/VA rating must be mentioned when ordering.

156

61
44
72

144

ATO-CT-3000

600/5 5 10 10 112510005

750/5 7.5 10 10 112512005

φ126.5
800/5 10 15 10 112515005
130.5
126.5

11
58

1000/5 10 15 10 112516005

1200/5 15 20 10 112520005
11
58
126.5 1500/5 15 20 10 112525005
130.5

2000/5 15 20 10 112530005

2500/5 15 20 10 112540005

3000/5 20 20 10 112550005

/ 20
225.5

20 10 112560005
42
67
57

Note: Class/VA rating must be mentioned when ordering.

192

Email: sales@ato.com
Phone: +1800-585-1519
Website: www.ato.com
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