Black Box IC109A-R2 Manual de Instalação descarregar pdf (Página 36)

63230-216-229-B1

Installation

1A/5A Current Transformers

Function

Connect Sepam™ to any standard 1A or 5A CT. Schneider Electric offers a range of

current transformers to measure primary currents from 50 A to 2500 A. Contact a

Schneider Electric representative for more information.

Current Transformer Sizing

Current transformers should be large enough to minimize saturation. CTs should be

selected per ANSI C37.110. This can be critical for high X/R systems with generators

larger than 2MW.

Normal Performance Higher Performance

Rated

Secondary

Current (i

Ratio

(1)

Burden

Designation

ANSI

Class

(2)

IEC

Class

(3)

Burden

Designation

ANSI

Class

(4)

IEC

Class

(3)

5 100/5 B-0.1 C10 2.5VA 5P20 B-0.2 C20 5VA 5P20

5 500/5 B-0.5 C50 15VA 5P20 B-1.0 C100 30VA 5P20

5 1200/5 B-2.0 C200 50VA 5P20 B-4.0 C400 100VA 5P20

1 100/1 B-0.1 C50 2.5VA 5P20 B-0.2 C100 5VA 5P20

1 500/1 B-0.5 C200 10VA 5P20 B-1.0 C400 30VA 5P20

1 1200/1 B-2.0 C1000

(5)

40VA 5P20 B-4.0 C2000

(5)

80VA 5P20

Transformer and Transformer-Machine Unit Differential Protection (ANSI 87T)

The phase CT primary currents must adhere to the following rule:

for winding 1.

for winding 2.

where:

S is the transformer’s rated power.

IN and I’N are the phase CT primary currents of winding 1 and 2 respectively.

LLn1

and V

LLn2

are winding 1 and 2 phase-to-phase voltages.

The rule of thumb is to size the primary and secondary CTR to 1.5XFLA. While the relay can

accept substantially smaller CTR's, care should be taken when the CTR is below the rated FLA.

Smaller CTR's generally result in a higher probability of saturation.

The current transformers should be defined by the knee-point voltage Vk ≥ (RCT + Rw) (20) iN.

The equation applies to the phase current transformer windings 1 and 2, where:

N and I’N are the CT rated primary and secondary currents respectively.

RCT is the CT internal resistance.

Rw is the resistance of the CT load and wiring.

Machine Differential (ANSI 87M)

Current transformers should be defined by a minimum knee-point voltage

Vk ≥ (RCT + Rw) (20)IN.

The equations apply to the phase current transformers placed on either side of the machine.

IN is the CT rated secondary current

RCT is the CT internal resistance.

Rw is the resistance of the CT load and wiring.

Generators are characterized by large X/R ratio's. The rule of thumb is to use the highest

possible accuracy class. A completely offset short circuit current requires the ct to support

(1+X/R) times the calculated voltage. In many applications it is not possible to completely avoid

saturation. Under these conditions it is helpful to have machine differential ct's with the same

knee point voltage

(1) CT ratio rule of thumb is to size primary to be 1.5 x connected load.

Example: 600/5. CT for 400A load.

(2) Typical usual product offering from switchgear manufacturers in North Americe for 50/51 products.

(3) Highest listed VA in IEC 60044 is 30VA

(4) Suitable for systems with X/R=15, or small generator connected to bus. Minimum for 87 protection.

(5) Not listed in C57.13

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