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(
)
S A and S C
---------------------------------------
1
2
3
±
Values between taps
3.4. Time Curves and Burden Data
3.4.1. Operating Time
The speed of operation is shown in Figure 10. The
curves indicate the time in milliseconds required for
the relay to provide an output for tripping after the
occurrence of a fault at any point on a line within the
relay setting.
Current Circuit Rating in Amperes
(All Ranges, All Settings)
Continuous — 10 Amperes
1 Second — 240 Amperes
3.4.2. Burden
The potential burden at 69 volts varies from a maxi-
mum of 1.4 volt-amperes at S = 1 setting to a mini-
mum of 0.42 volt-amperes based on 69 volts line-to-
neutral per phase. Current burden varies from a max-
imum of 4.5 volt-amperes at 5 amperes for a maxi-
mum T-setting to a minimum of 0.60 volt-amperes for
a minimum T-setting. This burden applies to each
phase and residual current circuit. Dc current burden
is .07 amperes at all rated voltages in non-trip condi-
tion.
3.4.3. Trip Circuit Constants
1 Ampere I.C.S. — 0.1 Ohms dc Resistance
4.
CALCULATIONS AND
SELECTION OF SETTING
Relay reach is set on the tap plate. Maximum sensi-
tivity angle, θ, is set for 75° (current lagging voltage)
in the factory. This adjustment need not be disturbed
for line angles of 65° or higher. For line angles below
65°. Set θ for a 60° maximum sensitivity angle, by
adjusting R
, R
, R
and R
1
2
3
dure for Zone1 application only. Set Zone1 reach to
be 85% of the line, if S = 1 is used; 75% if S = 2 or 3
are used. Do not change angle for pilot trip or Zone2,
or Zone3 applications.
Assume a desired balance point which is 85% of the
total length of the line. The general formulas for set-
ting the ohms reach of the relay are:
(
)
M A M B M C M O
,
,
,
------------------------------------------------------ -
.03
.09
.06
as per calibration proce-
4
0.85 R C
Z 1
=
Z 1 L
-------------------- - ; Z 0
R V
The terms used in this formula and hereafter are
defined as follows:
Z
= Zero sequence ohmic reach to be used for
0
relay settings.
Z
= Positive sequence ohmic reach to be used
1
for relay settings.
Z
,
= TS (1 + M) = the tap plate setting.
1
0
T
= Compensator tap value.
S
= Auto-transformer tap value.
θ
= Maximum sensitivity angle setting of the
relay.
±M
= Compensator tertiary tap value. (This is a
per unit value and is determined by the
sum of the values between the "L" and the
"R" leads. The sign is positive when "L:" is
above "R" and acts to raise the Z setting.
The sign is negative when "R" is above "L"
and acts to lower the "Z" setting).
Z
= Positive sequence ohms per phase of the
1L
total line section, referred to the primary.
Z
= Zero sequence ohms per phase of the total
0L
line section, referred to the primary.
R
= Current transformer ratio.
C
R
= Voltage transformer ratio.
V
The following procedure should be followed in order
to obtain an optimum setting of the relay.
Zone 1 Setting (SDG-1T and SDG-2T Relays)
1a.
Establish the desired values of Z
above (available from transmission line data)
and desired maximum sensitivity angle θ°.
1b.
Determine the desired tap plate value Z' using
the formula a:
I.L. 41-496.52D
0.85 R C
=
Z 0 L
-------------------- -
R V
and Z
as
1
0
7
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