DISTANCE RELAY PYTS

5.1) INTRODUCTION (MAIN FEATURES)

The main features of this relay are:-

- Mho characteristic, fully cross polarized, switched relay- so maximum accuracy

- As static circuits are used, so they have low burden on Ct’s and Pt’s.

- K 0 compensation available.

- RCA (relay characteristic angle) from 30 to 850 available.

- Three directional zones Z 1, Z 2, Z 3 and the fourth zone is starter, which is non
directional but option is available to make it directional too.

- Two types of starters are available

i) under impedance starters and

ii) Over-current starters.

- Single and three phase tripping available.

- SOTF, PSB, and distance relay schemes can be used.

- Minimum operating current required is 25 % of I n.

5.2) SETTING CALCULATIONS

Consider the following system

Conductor: Zigolo/ lynx Z = 0.689 750 ohms/ km

Pt ratio: 132 Kv/ 110 V

Ct ratio: 600/5

K0: 0.7

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Zone 1 = 85% of the first section i.e. AB

Z 1 Primary= 0.85 x 50 x 0.689 750

Z 1 Primary= 29.2 750 ohms

Z 2 Primary= AB complete + 50 % of BC

Z 2 Primary= 50 x 0.689 + 0.5 x 30 x 0.689

Z 2 Primary= 44.78 750 ohms

Z 3 Primary = AB complete + BC complete + 50 % of CD.

Very important to note that in zone 2, zone 3 and in zone 4, flexibility is allowed in settings.

Z 3 Primary= 50 x 0.689 + 30 x 0.689 + 0.5 x 45 x 0.689

Z 3 Primary = 70.64 750 ohms

Next Zone 4

Z 4 Primary = 110 % of Z 3

Z4 Primary = 1.1 x 70.64 = 77 ohms. (Angle does not apply as it is direction less)

Secondary values

UZ = (Pt ratio) / (Ct ratio) = (132000 / 110) / (600/5) = 10

Z1 secondary = Z1 Primary / U Z = 29.2 / 10 = 2.92 750 ohms

Z2 secondary = Z2 Primary / U Z = 44.78 / 10 = 4.478 750 ohms

Z3 secondary = Z3 Primary / U Z = 70.64 / 10 = 7.064 750 ohms

Z4 secondary = Z4 Primary / U Z = 77 / 10 = 7.7 ohms (angle does not apply)

Formula for the implementation of these values is as under:

Z1 = K1 x K Z x K D

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 K1 = 0.25, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0 (in some it has a
continuous adjustment).

KZ = has tapings of 0,1,2,3,5,10,20 ohms for 1 A

KD = Are range multipliers and are

0.1x,1 x,2 x, and ¥.

Z2 = K2 x K1x KZ x KD or Z2 = K 2 x Z1

K2 = 1, 1.2, 1.5, 2, 3, 4, 5, 10

Z3 = K3 x K1x KZ x KD or Z3 = K 3 x Z1

First we will set zone 1 such that

KZ x KD >= Z1

Hence we must have

KZ x KD >= 2.92

By checking the values for both K ‘s in above we see that we will have

KZ = 3 (it may not be available in some relays- they will have 4-so we will take 4)

and KD = 1

Thus 3 x 1>= 2.92

Or K1 x 3 x 1 = 2.92

K1 = 2.92 / 3 = 0.97

So zone 1 settings are KZ = 3, KD = 1 and K1 = 0.97

Zone 2 settings are

Z2 = K 2 x Z1

4.478 = K 2 x 2.92

K2 = 4.478 / 2.92 = 1.53

Zone 3 settings are

Z3 = K 3 x Z1

7.064 = K 3 x 2.92

K3 = 7.064 / 2.92 = 2.41.

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Zone 4 settings are

Z= K/ I

7.7 = K/ 5

7.7 * 5 = K

38.5 = K

All these settings of knobs on the relay will be set to achieve the desired settings. It is very important to note
that if a setting can not be implemented on a knob it is better to take the next higher so that the protection
zone is extended but care must be taken in zone 1, such that after extension zone 1 reach does not extend
beyond 90 % of the first section.

Other settings that are to be carried out are of K0 :

(Z L0-Z L1)/ (3ZL1) x Zone 1 settings = K1N x K ZN

K 0 x Zone 1 settings = K1N x K ZN

0.7 x 2.92 = 2.04

Therefore, select K1N and K ZN such that we get this value, and

K1N = 0.5 to 1.5 and

K ZN =

5.3) ADDITIONAL SETTINGS ON PYTS

:- module nos. 3

Link position A = Impedance starter.

B = When C.V.T is used with schemes

C = Over current starter.

:- module nos. 5

Link 2 – to make Z 4 directional or non directional

Link 6 – Blocking/ un-blocking starter tripping.

:- module nos. 6

Link 1 – Blocking/ un-blocking SOTF

Link 2 – Monitors SOTF through voltage and starters.

In PYTS relays there is another module for power swing settings. Although details of power swing
are to be explained in coming chapters but for the time being the settings are detailed below.

The outer reach of power swing circle is set on the left most module, while the inner circle will be that of Z 4.

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To set Z PS the formula is the same as that for Z 4. Just select reach in ohms as for Z and than apply the
following formula.

Z PS = K / I

There are some additional settings on the knob P

These are:-

K C knob is used for zone 1 extension scheme.

Knob P has the following settings

a Trip all zones.

b Power swing blocking in all zones.

c Trip in 1 and PSB in 2, 3, and 4

d Trip in 1 and 2 and PSB in 3 and 4.

e Trip in 1, 2, and 3 and PSB in 4

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