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FUNCTION CHARACTERISTICS

NG10 - Manual - 04 - 2022

CT supervision - 74CT - side H and side L

[1]

Preface

The CT monitoring function is employed to issue an alarm when secondary phase CTs and/or phase

input of the NT10 relay failure are detected. Interruptions are detected by means of a symmetry

criterion of the I

L1(H)

, I

L2(H)

, I

L3(H)

and

L1(L)

, I

L2(L)

, I

L3(L)

input currents.

The symmetry factor is calculated comparing the minimum and maximum of the fundamental compo-

nents of the three phase currents (I

LMIN(H)

/ I

LMAX(H)

for side H and I

LMIN(L)

/ I

LMAX(L)

for side L).

Operation and settings

The starting of the timer occurs if both the following conditions are ﬁlled:

A) I

LMIN(H)

/ I

LMAX(H)

) < S(H)<, that is the symmetry factor is lower than the S(H)<

adjustable thresh-

old for side H and I

LMIN(L)

/ I

LMAX(L)

) < S(L)<, that is the symmetry factor is lower than the S(L)<

adjustable threshold for side L;

B) I

LMAX(H)

> I(H)* for side H and/or I

LMAX(L)

> I(L)* for side L

Where

I(H)*, I(L)*: maximum phase current threshold

S(H)< S(L)<: element pickup value

S(H)

<, t

S(L)

operate time

After expiry of the associated operate time (t

S(H)

< for side H and t

S(L)

< for side L) a trip command is

issued; if instead the current drops below the threshold, the element it is restored.

The tripping characteristic is deﬁnite time.

The output may be assigned to the selected S(H)<TR-K output relays inside the Set \ CT supervision-

74CT- side H for side H and S(L)<TR-K output relays inside the Set \ CT supervision-74CT- side L for

side L menu; the same for addressing the LED indicators S(H)<TR-L and S(L)<TR-L.

The elements can be enabled or disabled by setting ON or OFF the 74CT(H)Enableparameter

inside the Set \ CT Supervision side H - 74CT side H menu for side H and 74CT(L)Enableparam-

eter inside the Set \ CT Supervision side L - 74CT side L menu for side L.

If the S(H)<-BLK1 and/or S(L)<-BLK1parameter is set to ON, and a binary input is designed for

logical block (Block1), the CT supervision function is blocked off whenever the given input is active.

The trip timer is held in reset condition, so the operate time counting starts when the input block

goes down.

[2]

All the parameters are common for A and B Proﬁle

Note 1 The H index that identify the variables related to the H side are indicated inside the schematic diagrams; the operation of the protection of

thermal imaging side L is similar to that of the side H.

Note 2 The exhaustive treatment of the logic block (Block 1) function may be found in the “Logic Block” paragraph inside CONTROL AND MONITORING

section

char74CT.ai

(H)

LMIN(H)

LMAX(H)

tgα=S

(H)

Current asimmetry monitoring - 74CT - side H

TRIP

NO TRIP

CT monitoring logic diagram - 74CT

Fun-74CT.ai

LMIN

LMAX

TRIPPING MATRIX

(LED+RELAYS)

Trip S<

Start I*

BLK1 S<

LMAX

>I*

Enable (ON≡ Enable)

Block1 input (ON≡ Block)

S<BLK1

Block1

Binary input INx

T 0

Logic

INx

OFF

n.o.

n.c.

INx

OFF

LMAX

LMIN

LMAX

S<TR-K

S<TR-L

RESET

Brand	Thytronic
Model	NG10
Category	Protection Device
Language	English

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