Name: Ring Type Current Transformer Protection Class Sensor
Brand: Asct Current Transformer
SKU: PR
Availability: InStock
Rating: 5 (1 reviews)

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Ring Type Current Transformer Protection Class Sensor

Description

Introduce

Replica currents are used as inputs to protective relays which will automatically isolate part of a power circuit in the event of an abnormal or fault condition therein, yet emit other parts of the plant to continue in operation.

Satisfactory operation of protective relays can depend on accurate representation of currents ranging from small leakage currents to very high overcurrent’s, requiring the protective current transformer to be linear, and therefore below magnetic saturation, at values up to perhaps 30 times full load current.

This wide operating range means that protective current transformer requires to be constructed with larger cross-sections and heavier cores than equivalent current transformers used for measuring duties only.

Features

Tough resilient flame retardant.

Tropicalized design with Insulation Class A and thermal 105°C

Totally enclosed in tough with self-extinguishing.

Specification

Dimensions

Type	Ratio	ID(mm.)	OD(mm.)	Burden of class 5P10					Burden of class 5P20
				5	7.5	10	15	20	5	7.5	10	15
				HT Thickness(mm.)					HT Thickness(mm.)
PR-30	60	30	80	35	35	-	-	-	35	35	-	-
	80	30	80	35	35	-	-	-	35	35	-	-
	100	30	80	35	35	-	-	-	35	35	-	-
	150	30	80	35	35	35	-	-	35	35	35	-
	200	30	80	35	35	35	-	-	35	35	35	-

Type	Ratio	ID(mm.)	OD(mm.)	Burden of class 5P10					Burden of class 5P20
				5	7.5	10	15	20	5	7.5	10	15
				HT Thickness(mm.)					HT Thickness(mm.)
PR-40	150	40	100	35	35	35	-	-	35	35	35	-
	200	40	100	35	35	35	-	-	35	35	35	-
	250	40	100	35	35	35	-	-	35	35	35	-
	300	40	100	35	35	35	-	-	35	35	35	-
	400	40	100	35	35	35	-	-	35	35	35	-

Type	Ratio	ID(mm.)	OD(mm.)	Burden of class 5P10					Burden of class 5P20
				5	7.5	10	15	20	5	7.5	10	15
				HT Thickness(mm.)					HT Thickness(mm.)
PR-45	200	45	100	35	35	35	-	-	35	35	-	-
	250	45	100	35	35	35	35	-	35	35	-	-
	300	45	100	35	35	35	35	-	35	35	-	-
	400	45	100	35	35	35	35	-	35	35	35	-

Type	Ratio	ID(mm.)	OD(mm.)	Burden of class 5P10					Burden of class 5P20
				5	7.5	10	15	20	5	7.5	10	15
				HT Thickness(mm.)					HT Thickness(mm.)
PR-60	400	60	100	35	35	35	35	-	35	35	35	-
	500	60	100	35	35	35	35	35	35	35	35	-
	600	60	100	35	35	35	35	35	35	35	35	35
	800	60	100	35	35	35	35	35	35	35	35	35

Type	Ratio	ID(mm.)	OD(mm.)	Burden of class 5P10					Burden of class 5P20
				5	7.5	10	15	20	5	7.5	10	15
				HT Thickness(mm.)					HT Thickness(mm.)
PR-70	600	70	115	35	35	35	35	35	35	35	35	35
	800	70	115	35	35	35	35	35	35	35	35	35
	1000	70	115	35	35	35	35	35	35	35	35	35
	1200	70	115	35	35	35	35	35	35	35	35	35

Type	Ratio	ID(mm.)	OD(mm.)	Burden of class 5P10					Burden of class 5P20
				5	7.5	10	15	20	5	7.5	10	15
				HT Thickness(mm.)					HT Thickness(mm.)
PR-85	800	85	125	35	35	35	35	35	35	35	35	35
	1000	85	125	35	35	35	35	35	35	35	35	35
	1200	85	125	35	35	35	35	35	35	35	35	35
	1600	85	125	35	35	35	35	35	35	35	35	35

Type	Ratio	ID(mm.)	OD(mm.)	Burden of class 5P10					Burden of class 5P20
				5	7.5	10	15	20	5	7.5	10	15
				HT Thickness(mm.)					HT Thickness(mm.)
PR-110	1200	110	155	35	35	35	35	35	35	35	35	35
	1600	110	155	35	35	35	35	35	35	35	35	35
	2000	110	155	35	35	35	35	35	35	35	35	35
	2500	110	155	35	35	35	35	35	35	35	35	35

Type	Ratio	ID(mm.)	OD(mm.)	Burden of class 5P10					Burden of class 5P20
				5	7.5	10	15	20	5	7.5	10	15
				HT Thickness(mm.)					HT Thickness(mm.)
PR-120	1600	120	165	35	35	35	35	35	35	35	35	35
	2000	120	165	35	35	35	35	35	35	35	35	35
	2500	120	165	35	35	35	35	35	35	35	35	35
	3000	120	165	35	35	35	35	35	35	35	35	35

Type	Ratio	ID(mm.)	OD(mm.)	Burden of class 5P10					Burden of class 5P20
				5	7.5	10	15	20	5	7.5	10	15
				HT Thickness(mm.)					HT Thickness(mm.)
PR-130	2500	130	175	35	35	35	35	35	35	35	35	35
	3000	130	175	35	35	35	35	35	35	35	35	35
	3500	130	175	35	35	35	35	35	35	35	35	35
	4000	130	175	35	35	35	35	35	35	35	35	35

Type	Ratio	ID(mm.)	OD(mm.)	Burden of class 5P10					Burden of class 5P20
				5	7.5	10	15	20	5	7.5	10	15
				HT Thickness(mm.)					HT Thickness(mm.)
PR-140	2500	140	185	-	-	-	35	35	-	-	-	35
	3000	140	185	-	-	-	35	35	-	-	-	35
	3500	140	185	-	-	-	35	35	-	-	-	35
	4000	140	185	-	-	-	35	35	-	-	-	35

Type	Ratio	ID(mm.)	OD(mm.)	Burden of class 5P10					Burden of class 5P20
				5	7.5	10	15	20	5	7.5	10	15
				HT Thickness(mm.)					HT Thickness(mm.)
PR-170	3000	170	205	-	-	-	35	35	-	-	-	35
	3500	170	205	-	-	-	35	35	-	-	-	35
	4000	170	205	-	-	-	35	35	-	-	-	35
	5000	170	205	-	-	-	35	35	-	-	-	35
	6000	170	205	-	-	-	35	35	-	-	-	35

Type	Ratio	ID(mm.)	OD(mm.)	Burden of class 5P10					Burden of class 5P20
				5	7.5	10	15	20	5	7.5	10	15
				HT Thickness(mm.)					HT Thickness(mm.)
PR-190	3500	190	230	-	-	-	35	35	-	-	-	35
	4000	190	230	-	-	-	35	35	-	-	-	35
	5000	190	230	-	-	-	35	35	-	-	-	35
	6000	190	230	-	-	-	35	35	-	-	-	35
	8000	190	230	-	-	-	35	35	-	-	-	35

Type	Ratio	ID(mm.)	OD(mm.)	Burden of class 5P10					Burden of class 5P20
				5	7.5	10	15	20	5	7.5	10	15
				HT Thickness(mm.)					HT Thickness(mm.)
PR-220	4000	220	260	-	-	-	35	35	-	-	-	35
	5000	220	260	-	-	-	35	35	-	-	-	35
	6000	220	260	-	-	-	35	35	-	-	-	35
	8000	220	260	-	-	-	35	35	-	-	-	35

Type	Ratio	ID(mm.)	OD(mm.)	Burden of class 5P10					Burden of class 5P20
				5	7.5	10	15	20	5	7.5	10	15
				HT Thickness(mm.)					HT Thickness(mm.)
PR-250	4000	250	290	-	-	-	35	35	-	-	-	35
	5000	250	290	-	-	-	35	35	-	-	-	35
	6000	250	290	-	-	-	35	35	-	-	-	35
	8000	250	290	-	-	-	35	35	-	-	-	35

Type	Ratio	ID(mm.)	OD(mm.)	Burden of class 5P10					Burden of class 5P20
				5	7.5	10	15	20	5	7.5	10	15
				HT Thickness(mm.)					HT Thickness(mm.)
PR-270	4000	270	310	-	-	-	35	35	-	-	-	35
	5000	270	310	-	-	-	35	35	-	-	-	35
	6000	270	310	-	-	-	35	35	-	-	-	35
	8000	270	310	-	-	-	35	35	-	-	-	35
	10000	270	310	-	-	-	35	35	-	-	-	35

Type	Ratio	ID(mm.)	OD(mm.)	Burden of class 5P10					Burden of class 5P20
				5	7.5	10	15	20	5	7.5	10	15
				HT Thickness(mm.)					HT Thickness(mm.)
PR-300	4000	300	340	-	-	-	35	35	-	-	-	35
	5000	300	340	-	-	-	35	35	-	-	-	35
	6000	300	340	-	-	-	35	35	-	-	-	35
	8000	300	340	-	-	-	35	35	-	-	-	35
	10000	300	340	-	-	-	35	35	-	-	-	35

CAUTION: RELAY MANUFACTURER’S RECOMMENDATIONS SHOULD ALWAYS BE FOLLOWED.

For space and economy reasons, equipment designers should , avoid over-specifying protective current transformers. To specifying protective CT's and require some or all of the following information:

(a) Protected equipment and type of protection.

(b) Maximum fault level for stability.

(d) Type of relay and likely setting.

(e) Pilot wire resistance, or length of run and pilot wire used.

(f) Primary conductor diameter or bulbar dimensions.

Accuracy

Accuracy Limit Factor is defined as the multiple of rated primary current up to the transformer will comply with the requirements of 'Composite Error'.

Composite Error is the deviation from an ideal CT (as in Current Error), but takes account of harmonics in the secondary current caused by non-linear magnetic conditions through the cycle at higher flux densities Standard Accuracy Limit Factors are 5, 10, 15, 20 and 30.

The electrical requirements of protection current transformer can therefore be defined as: Ratio / VA Burden / Accuracy Class / Accuracy Limit Factor.

Class 5P and 10P protective current transformers are generally used in overcurrent and unrestricted earth leakage protection. With the exception of simple trip relays, the protective device usually has an intentional time delay, thereby ensuring that the severe effect of transients has passed before the relay is called to operate.

Protection Current Transformers used for such applications are normally working under steady state conditions.

Three examples of such protection is shown.

Three Phase Overcurrent Protection.

Unrestricted ground fault protection

(Detects ground fault on CT load side)

Combined 3Phase & Unrestricted EarthFault Protection

In some systems it may sufficient to simply detect a fault and isolate that circuit.

However, in more discriminating schemes, it is necessary to ensure that a phase-to-phase fault does not operate the earth fault relay.

Phase Fault Stability

Current transformers which are well matched and operating below saturation, will deliver no current to the earth fault relay, since 3-phase currents sum to zero.

If however, the transformers are badly matched, a spill current will arise which will trip the relay. Similarly, current transformers must operate below the saturation region, since, in a 3-phase system, third harmonics in the secondary are additive through the relay, thereby creating instability and erroneously tripping the earth fault relay .

Balanced Protection

In balanced systems of protection, electrical power is monitored by the protective CTs at two points in the system as shown.

The protected zone is between the two CTs.

If the power out differs from the power in, then a fault has developed within the protected zone and the protection relay will operate. A 'Through Fault' is one outside the protected zone.

Should such a fault occur, the relay protecting the protected zone will not trip, since the power out will still equal the power in.

Numerous different types of balanced systems exist and advice may often have to be obtained from the relay manufacturer. However, in all cases Sensitivity and Stability must be considered.

Transient Effects

Balanced protective systems may use time lag or high speed armature relays. Where high speed relays are used, operation of the relay occurs in the transient region of fault current, which includes the d.c. asymmetrical component. The buildup of magnetic flux may therefore be high enough to preclude the possibility of avoiding the saturation region.

The resulting transient instability can fortunately be overcome using some of the following techniques:

(a) Relays incorporating capacitors to block the dc asymmetrical component.

(b) Biased relays, where dc asymmetrical currents are compensated by anti-phase coils

(c) Stabilizing resistors in series with current operated relays, or in parallel with voltage-operated relays. Threes limit the spill current (or voltage) to a maximum value below the setting value.

For series resistors in current operated armature relays.

Rs = Vkp - VA

2Ir/Ir

Where Rs = value of stabilizing resistor in ohms Vkp = CT knee point voltage VA = relay burden (typically 3VA) Ir = relay setting current

The value of Rs varies with each fault setting. An adjustable resistor is therefore required for optimum results. Often a fixed resistor suitable for mid-setting will suffice.

Sensitivity

Sensitivity is defined as the lowest value of primary fault current, within the protected zone, which will cause the relay to operate. To provide fast operation on an in-zone fault, the current transformer should have a 'Knee-Point Voltage' at least twice the setting voltage of the relay.

The 'Knee-Point Voltage' (Vkp) is defined as the secondary voltage at which an increase of 10% produces an increase in magnetizing current of 50%.It is the secondary voltage above which the CT is in magnetic saturation. Differential relays may be set to a required sensitivity but will operate at some higher value depending on the magnetizing currents of the CTs, for example:

The diagram shows a restricted earth fault system with the relay fed from 400/5 CTs.

The relay may be set at 10%, but, it requires more than 40A to operate the relay, since the CT in the faulty phase, has to deliver its own magnetizing current and that of the other CTs in addition to the relay operating current.

Where

Primary Operating Current (P.O.C.) = K(Ir + nle)

K = CT Ratio

Ir = Relay set current

Ie = CT magnetizing current

n = Number of CTs in parallel.

E/Fault Relay, set to trip at 10% Nutral CT Supplies ie.

40A Pri. Fault, will not trip until Relay+ Mag.

Current fault is 56A. Of four CT’s

That quality whereby a protective system remains in-operative under all conditions other than those for which it is designed to operate, i.e., an in-zone fault. Stability is definded as ratio of the maximum though foult cuurent at which the system is stable to nominal full load cuurent.

Good quality current transformers will produce linear output up to the defined kneepoint voltage (Vkp).

Typically,

Vkp = 2lf (Rs + Rp) for stability,

Where If = max. through fault secondary current at stability limit Rs = CT secondary winding resistance RP = loop lead resistance from CT to Relay

Technical Parameter

Temperature range	–20°C to 70°C
Protection class	5P10, 5P20 etc.
Test voltage	4Kv 50Hz. 1min.
Operating voltage	0.66 KV
Secondary	1A or 5A
Standard	EC44-1, IEC185, BS3938, DIN42600