GE GCY51F Series User manual

I
N
ST RU C T ION
S
MHO
Distance
Relay
Type
GCY51F
GEK-26437B
Supersedes
GEK-2643Th
GENERALS
ELECTRIC

DESCRIPTION
APPLICATION
.
RATINGS
ONE
SECOND
RATINGS
AND
H 2
OFFSET
H 1
AND
N 2
TAP LOCATIONS
12GCY51F1A
12GCY5IF2A
CONTACTS
TARGET/SEAL-IN
UNIT
BURDENS
12GCY51F1A
CURRENT
CIRCUITS
POTENTIAL
CIRCUITS
H 1
UNIT
M 2
UNIT
12GCYS1F2A
CURRENT
CIRCUITS
POTENTIAL
CIRCUITS
H 1
UNIT
M 2
Unit
CALCULATION
OF
SETTINGS
OPERATING
PRINCIPLES
H 1
UNIT
H 2
UNIT
CHARACTERISTICS
H 1
UNIT
IMPEDANCE
CHARACTERISTIC
UNDERREACH
MEMORY
ACTION
TRANSIENT
OVERREACH
...
OPERATING
TIME
UNIT
IMPEDANCE
CHARACTERISTIC
UNDERREACH
MEMORY
ACTION
TRANSIENT
OVERRREACH
OPERATING
TIME
CONSTRUCTION
CASE
GENERAL
ELECTRICAL
TESTS
DRAWOUT
RELAYS
GENERAL
POWER
REQUIREMENTS
GENERAL
RECEIVING,
HANDLiNG
AND STORAGE
PERIODIC
CHECKS
AND ROUTINE
MAINTENANCE
CONTACT
CLEANING
MECHANICAL
INSPECTION
SERVICING
CONTROL
SPRING
ADJUSTMENT
CLUTCH
CHECKS
CLUTCH-ELECTRICAL
TESTS
BASIC
MINIMUM
REACH
TESTS
ANGLE
OF
MAXIMUM
TORQUE
REACH
TAP CHECK
M 1 -M 2
OFFSETS
TESTS
TARGET/SEAL-IN
INSTALLATION
PROCEDURE
LOCATION
MOUNTING
CONNECTIONS
RENEWAL
PARTS
GE
K-254
37
CONTENTS
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2

GEK-26437
MHO
DISTANCE
RELAY
TYPE
GCY5IF
DESCRIPTION
The
GCY51F
is
a
single—phase
inho
relay
consisting
of
two
units
and
associated
auxiliaries
mounted
in
the
large
(La)
double-ended
case.
The
lower
unit
is an
M 1
unit
which
is designed
for
first
zone
application.
The
upper
unit
is an
M 2 unit
which
is
designed
for
second
zone
applications
only.
The
second
zone
is
offset
in
the
forward
direction
to
provide
a
figure
8”
characteristic
suitable
for
ling,
heavily
loaded
lines. GEK-26437
covers
a
5 ampere,
60
hertz
model (Form
1A)
and
a
1 ampere,
50
hertz
model (Form
2A).
The
impedance ranges
and
offsets
are
shown
in Table
I.
Since
the
one
ampere
relay
has
five
times
the
impedance
range
of the
five
ampere
relay,
the
application
and
calculation
of
setting
discussion
is
applicable to
the
one
ampere
relay
by multiplying
the
impedances
by
five.
The
internal
connections
diagram
is
as
shown
in
Figure
13.
APPLICATION
The
GCY51F
relay
is
used
for
phase
fault
protection
of
a
transmission line.
It
has
a distinctive
figure
eight’
characteristic
which
is
obtained by using
two
separate
mho
units
per
phase
of the
line.
The
first
zone
mho
unit,
M 1 ,
has
a characteristic
which
passes
through the origin
of
the
R-X
diagram
as
in the
usual
application.
The
characteristic
of the
second
zone
mho
unit,
M 2 ,
s
offset in
the
forward
direction
by
an
adjustable
amount which
allows
overlapping
of
the
two
characteristics.
See
the
R-X
plot
o
the
character
istics in
Fig.
11.
The
‘figure
eight’
characteristic
is
applied
where
a relay
with
a
long
forward reach
setting
is
required
and
at the
same
time
it is
necessary to
accoirmiodate
heavy
line
loadings
or
nhinor
system
swings
without
caus
ing
relay
operation.
The
M 1
first
zone
unit
may
be
used
alone to provide
instantaneous tripping
for
a
portion
of
the
protected
line.
The
N 2 second
zone
unit
is
used
with
a timer
to provide
time-delay
back-up tripping
for
the balance of
the
protected
line
and
a
portion
of the
next
line
section.
The
trip
contacts
of
both
units
connected in
parallel will
provide the
overreaching tripping
characteristic
needed
for
directional
comparison
or
trans
ferred
tripping
pilot—relaying
schemes.
Typical external
connections are
shown
in
Figs.
l6A
and
B
for
the
scheme
of
protection described.
This
shows
the
need
for auxiliaries
such
as
a timer
and
a tripping
rectifier
for
circuit
isolation
in
addition
to
the
auxiliaries
needed
for
whatever
type
of
pilot-relaying
scheme
is
selected.
If
the
GCYS1F
is
used
in a
pilot-relaying
scheme
with
the line
side
potential
and
high speed reclosing,
it
is
recorrieended
that
overcurrent
fault
detectors be used
to
supervise the
trip
circuits.
When
setting
the
relay
units,
it
is reconnended
that
the
offset
setting
on
the
M 2
unit
not
exceed
80
per
cent
of tho
forward
reach
setting
of
the
Ml
unit.
This
will
insure
at
least
a 20
percent
overlap
of
the
two
characteristics
based
on
the
reach
setting
of
the N 1
unit.
When
selecting
a
basic
minimum
ohmic
reach
tap
to
protect
a
line,
it
is
desirable
to
select
the
highest
one
that
will
accoriiriodate the
desired
setting. For
example,
if
a
5
ohm
setting
is desired
on the
M 1
unit,
the tap
selected should
be
3
ohms
minimum
rather
than
the
0.75
or
1.5
ohm
tap.
This
will
insure
the
highest
possible
torque
level
in
the
relay.
Refer
to
the
sec
tion
on
CALCULATION
OF
SETTINGS for
a
worked
example
of
determining the
required
settings
for
a
typical
application.
Refer
to
the
section
on
CHARACTERISTICS
for
the
relay
unit
operating
time
curves,
Fig.
8
and
Fig.
10
and
the
relay
reach
vs.
fault
current
curves
in Fig.
7
and
Fig.
9.
In
the
normal
transmission
line
application
the
N 1
first
zone
unit
reverse
offset
is set
at
zero.
Thus,
this
unit
will
operate
for
faults
only
in
the
protected
line
section
and
not
operate
for
bus
faults
behind
the
relay
location.
However,
when
the
protected
line
ends
in
a transformer
and
the
relay
is
connected to
CT’s
and
PT’s
on
the
line
side
of
the
transformer,
the
M 1
first
zone
reverse
of,set
may be
set at
0.5
ohm
so as
to
reach
backwards
part
way
into
the
impedance of
the
transformer
bank.
Thus,
the
relay
will
remain
picked
up
even
for
a
zero
voltage
line
fault
right
at
the transformer terminals
independent of
first
zone
memory
action.
The;e
instructions
do
not
purport to cover
all
details or
variations in
equipment
nor
to
provide
for
ever.;
possbie contingency
to
be met
in
connectIon
with
installation,
operation or
maintenance.
Should
further
information
be
desired
or
should
particular
problems
arise
which
are
not covered
sufficicntly
for
the
purchaser’s
purposes,
the
matter
should
be
reterz-ed
to
the
General
Electric
Company.
To
the
extent
required
the
products described herein
meet
applicable
ANSI,
IEEE
and
NEMA
standards;
but
no
such
assurance
is
given
with
respect
to
local
codes
and ordinances
because they
vary
greatly.
3

GEK-26a37
RATINGS
-
c-stance
relays
are
rated
as
follows
DE
SECOND
RATINGS
The
one
second
ratings
of
the
current
circuits of
the
12GCY51F(-)A
relays
are
listed
below.
K =
12 t
rating chart.
TABLE
I
equation
12GCY51F1A
J
BASIC MIN.
OHMIT
ANGLE
MAX. OFFSET
RANGE
ANGLE
OF
UNIT
4
REACH
0-N__—
RANGE
jJRQUE
0—N
OFFSET
Ml
.75/1.5/3.0
0.75-30
60-75°
Lag
0/0.5
Ohm
255°
Lag
M 2
1/2/3
1.0
—3.0
60-75°
Lag
0—4
Ohms
750
Lag
— —__________
(1.0
Ohm
steps)
TABLE
II
12SF
Y51F2J\
______
____________
_____
________
___________
_______________
r
UASIC
MIS.
OFFSEF
RANGE
ANGLE
OF
UNIT
REACH
0-N 0-N
OFFSET
3.75/7.5/15
3.75-150 60-75° Lag
0/2.5
Ohms
255°
Lag
N 2
5/10/15
5.0
—150 60—75°
Faq
0—20
Ohms
75°
Faq
L
___L”_steps)
__
__
Thcsc
rridys
are
factory
adjusted
br
the
basic
minimum reach
dt
the
75
deqree
lag,
angle
ot
maximum
rJr’JIC
1-1
though
the
units
can
he
adjusted to a
60
degree
lag,
angle
of
maximum
torque,
a reduction
of
the
ciii
urn
reash
can
be expected.
self’,
at
600
lag
3
reduction
in reach.
jri
:.
at
GO°
lag
2O
reduction
in
reach.
Other
magnitudes
of
current
can
be
applied
for
various
periods
of
time
by
applying
the
following
t=
The
and
II.
Constant.
(See
one
second
Applied
current
(rms).
Time
(Seconds).
basic
minimum reach
range,
angles
of
maximum
torque,
offset
range
and
angle
are
listed
in
Tables
I
OHMIC
0—14
H
AN
C L
ANGLE
MAX.
TORQUL
4

GEK-26437
The
basic
minimum
reach can
hr
extended
up
to
the
maximum
ohmic
0—H
reach
by
reducing
the
uri’c
restraint
transformer.
This
can
be
accomplished
by
applying
the following
equation.
Transf.
setting
()
1P
---)_X
ba 4 ’
“nium
rech
tap.
Z
—N
Z
0-N
= desired
reach
Basic
iciminmum
reach
tap
=
select
the
highest
reach
tap
below
the
Z 0-N
setting
desired.
M 1
and
N 2 _Offset
The M 1
unit
has
a
reverse
offset,
where
the
forward
reach
of
the
unit
is
maintained
and
the
insertirn
of
an
offset
increases
the
diameter
of
the
characteristic
so
that
it
extends
in
a
reverse
direction,
providing
an
offset
equal
to
the
offset
tap
selected
(+)
10
percent.
The
M 2
unit
has
a
forward
offset,
where
the
diameter
of
the units
characteristic
is
moved forward
along
the
unit’s
angle
of
maximum
torque,
equal
to
the
offset
tap
(+)
10
percent.
and
M 2
Tap
Locations
12PCY51F1A
The N 1
unit
reach taps
are
located
on
two
tap
plates
and
block
located
to
the
right
of
the
Ml
unit
(lower
unit).
The
basic
minimum
reach
taps are
marked
on
the
plate.
The
taps
are
selected
by
two
insulated
tap
screws
and
should
be
set
identically
for
a particular
reach
setting.
The
M 1
offset
tap is
located
at
the
rear of
the
relay
behind
the
M2
unit
(upper
unit).
The
offset
is
a
fixed
value
and
is
selected
by
a
link
in
an
‘In”
or
Out’
consideration.
The N 1
unit
restraint
transformer
is
located
on
the
left
side
of
the
relay
front
view.
It
has
taps
in
one
percent
dnd
10
percent
steps
which
are
selected
with
two
insulated
tap
plugs
and
movable
jumper
leads.
The
N 2
unit
reach
taps are
located
behind
the relay
on
a
Bakelite
tap
block,
using
links
to
obtain
the
basic minimum
reach.
Both
sets
of
links
must
be
set identically
for
any
basic
reach
desired.
Table
HI
indicates
the
connections
for
the
basic
minimum
reach
setting.
TABLE
III
RELAY
BASIC
MINIMUM A”
“B”
MODEL
REACH
0-N
LINKS
LINKS
1
Ohm
1
0
GCY51F1A
2
Ohms
0
2
3Ohms
1
2
5Ohms
5
0
GCY51F2A
10
Ohms
0
10
l5Ohms
5
j
10
The
M 2
unit
offset
is
located
at
the
front
of the
relay
just above
the N 2
unit.
The
offset
taps are
marked
--0, 1, 2, 3,
4
ohms and
are
selected
by
a
sliding
lead
and
captured
screw.
The N 2
restraint
transformer
is
located
on
the right
side
of
the
relay
front view.
It
consists
of
a
ta
block with
taps ranging
in
one
percent
steps
and
in
ten
percent
steps.
The
tans arr
selected
with
two
insu
lated
tap pluqs
and
movable
jumper
leads.
12GCYB1F2A
The
location
of
units and
components
of
the
12GCY51F2A
is
the
same
as
in
the
12GCY51Fi
relay,
except
that
it
is
used
with
one
ampere
current transformers,
with th
Dhmic range
equai
to
five
times
the 12GCYS1F1A
relay.

GEK-26437
Contacts
The contacts of
these
distance relays
when closed due
to
a fault, will momentarily carry
30 amperes up
jltS d-c.
However,
the
circuit
breaker trip circuit must be opened by an auxiliary switch or
by
some
other
suitable
means since the relay contacts
do not have an interrupting
rating.
Target/Seal-in Unit
The
relays have a 0.6/2.0
ampere d-c tap rating.
The
electrical parameters
are listed
in Table
IV.
TABLE IV
TARGET
SEAL-IN
UNIT
0.6
AMP TAP
2.0
AMP TAP
Minimum Operating 0.6
amps
2.0
amps
Carry Continuously 1.5
mps
3.5
amps
Carry 30 Amps for 0.5 secs. 4 secs.
Carry 10 Amps for
4
secs. 30
secs
0-C Resistance
0.6
ohms
0.13 ohms
60 Cycle Impedance 6
ohms
0.53
ohms
BURDENS
Current Circuits
The
maximum
current burden Imposed
on
each
GCY51F(-)A
relays
is
shown in
Table V.
AMPS HERTZ R X P.F. W.
5 60 0.3
0.05
0.98 7.5
7.6
This data
is for
the 3.0 ohm basic reach tap
of
the M 1 and M 2 units.
The
burden
with the
M 1
unit in
the 1.5 or 0.75 ohm tap or
with
the M 2 unit in the 2 or
1 ohm
tap
will be
slightly
lower.
Potential Circuits
The
maximum
potential
burden imposed on
each
potential transformer at
120 volts,
60
hertz
Table VI
for restraint
transformer
settings at 100 percent.
TABLE VI
is shown in
CIRCUIT
I
R
JX
P.F.
WATTS
V.A.
M 1
Restraint 3200
JO 1.0
4.5 4.5
N 1 Polarizing 1300 -J680
0.89
8.7 9.8
M 2
Restraint
1150 +J]370
0.64
5.2 8.1
M 2 Polarizing 1440 -J217 0.99 9.7 9.8
The potential burdens at
restraint
from toe following
formula.
transformer
settings
of
less than 100 percent
can he
calculated
, Unit
VA
(a
+ Jb)rMl
tap
setting()1
2
+ (C + Jd)
[input
tap
setting
(j_J
1 2GCY51 F1A
current transformer
at
five amperes for a
set of three
TABLE V
6

GEK-26437
TI 2
Unit
VA
=
(e
+
if)
rM2
tap
setting
()
1
2
+ Jh)
Linput
tap
setting
(%)J
The
terms
(a
+ Jb),
(C
+
Jd)
etc.
represent
the
burdens
of
the
Mi
and
M 7
potential
circuits
expressed
in
watts
and
vars
with
the
restraint
taps
in
100
percent.
Table
VII
gives
the
values
for
these
tenlis.
TABLE
VII
1
CIRCUIT
TERM
(WATTS
+
J
VARS)
(WATTS
+ 3
VARS)
TI 1
Restraint
a +
Jb
4.5
+
JQ
Mi
Polarizing
c +
Jd
8.7
-
34.5
M 2
Restraint
e
+ if
5.2
+
J6.2
M 2
Polarizing
y
+
Jh
9.7
—
31.5
Total
burden
can
be
obtained
by
adding
the
M 1
and
M 2
watts
and
vars
for
each
unit
as
determined
by
the
above
Table
VII and
converting
the
total
to
volt-amperes.
1
2GCY51
F2A
Current
Circuits
The
maximum current
burden
imposed
on
each
current
transformer
at
one
ampere
for
a set
of
three
relays
is
listed
in
Table
VIII.
The
data
is for
a
relay
set
at
the
maximum
reach
taps.
TABLE
VIII
AMPS
HERTZ
R
X
P.F.
WATTS
V.A.
1
50
11.90
16.40
0.587
11.90
20.27
Potential Circuits
CIRCUIT
R
ix
P.F.
WATTS
V.A.
VARS
TI 1
Restraint
19.60
32279
3.652 3.12
4.78
3.62
M 1
Polarizing
14.53
-3817
0.872 7.53
8.63 —4.21
TI 2
Restraint
11.65
31866
0.53
3.46 6.52
5.52
TI 2
Polarizing
15.42
-J769
0.89 7.34 8.25
-3.26
The
potential
burdens
at
restraint
transformer settings
of
less
than
100
percent
can
be
calculated
from
the
following
equations.
M 1
Unit
VA
= (a
+
Jb)EM1
tap
setting
()
1
2
+
(C
+
3d)
[input
tap
setting
(%)]
TI 2
Unit
VA
(e
+
Jf)r2
tap
setting
2
+
+ Jh)
Linput
tap
setting
(‘)J
The
terms
(a
+ 313)
to
(g
+
JH)
represent
the
burdens
of
the
Ml
and
TI 2
potential
circuits
expressed in
watts and
vars
with the
restraint
taps
in
100
percent.
Table
X
lists
the
values
of
these
terms.
The
input
tap
settings
in
the
above
equations are
100
percent.
7
TABLE
IX

GEK-26437
TABLE X
CIRCUIT
TERM
WATTS
+ J
VARS
WATTS
+ J
VARS
-
H 1
Restraint
a + Jb 3.12
+ J3.62
M 1 Polarizing
C
(+) Jd
7.53
- J4.2l
H 2
Restraint
e + Jf
3.46
+ J5.52
H 2
Polarizing
g
(±)
Jh
7.34
- J3.76
The total
burden
can be obtained by
adding
the
H 1 and N 2
watts
and
vars for
each
unit
as
listed In
Table
X
and
converting to
volt—amperes as
indicated
in the
equations
for
transformer
settings
less than 100
percent.
The maximum burden
imposed on the potential
transformer by
the
offset
transactor
in addition to
the
unit’s
burden
in
Table IX is shown
In XI.
TABLE
XI
R
JX
P.F. WATTS
V.A.
VARS
7.66
11.59 0.66 7.66
11.60
8.72
If offset
is used
the volt-amperes
of the
offset
transactor must be
added
to the
M 1 and N 2
units
volt
amperes to
determine
the maximum
volt
amperes
of the relay’s potential
circuit
with offset.
CALCULATION
OF SETTINGS
The
following
is a typical
worked example
of how
to
determine
the reach and offset
tap
settings
for the
relay to
provide the
proper line
protection.
Assume
a
230kV line
100 miles long with
a positive sequence
primary
impedance
of
Z(pri)
= 8O
With a CT ratio of
1200/5
and
a
PT
ratio
of
2000/1
the
secondary impedance
becomes
CT
Ratio
Z(sec)
= Z(pri) X
PT Ratio
Z(sec)
ohms
Set the M 1
first
zone
unit to
90
percent of
the protected line section
taking
into
account the
dif
ference
between
the line
angle
0
= 85
degrees
and
the H 1 angle of maximum
torque 9 = 75
degrees by the func
tion
of cos
(0—9).
The
N 1
reach at
its angle of
maximum torque should
be
- 0.90 x 9.6
— 8.64
—
—
— 8.77
ohms
Using the three
ohm
basic minimum
reach tap, the
N 1
tap
setting
will
be
TAP
(M 1 )
= —-
= 34
Assume that
we
are
using
a relay
where the
N 2
unit has
a 0-4 ohm forward
offset
range.
It
is obvious
that with
a
full four
ohm offset, the
overlap with
the H 1 unit
reach set
at 8.83
will
be ample. Set the
M,
rit
to reach
approximately
150
percent
of
the protected line
section
with zero
infeed at the
remote
bus
again
taking
into
account the
difference
in line
ano 1 e with maximum
torque
angle. The M 2 reach
at
its
angle
c airnur torque
will
then be
Reach
(N
)
1.5(9.6)
14.62
/75°
2
cus 10°
8

GEK-26437
The
approximit.e
diaiieter
of
the
M
cheracteristic
will
then
he
this
redch
minus
the
four
ohms
offset
at
75
degrees
or
Z
(M 2 )
= 14.6? -
4.0
10.E?
Again
using
the
three
ohm
basic
minimum
reach the
M 2
tap
setting
will
be
TAP
(M 2 )
10.62
=
281
This
calculation
of
the
setting
of M
2
is
not
n
exact solution
but
may
be
close
enough
for
all
prac
tical
purposes
since
it
is
the
setting
on
overreaching
second zone
characteristic.
The
smaller
the
angular
difference
between
the
line
and
the
relay
angle
of
maximum
torque, the
smaller
the
error
in
the
reach.
Conversely
time
larger
the
amount of
forward
offset that
is
used for
M 2 ,
provided
there
is
an
angular
dif
ference,
the
greater
the
error.
To
check
the
calculitions
it
is
always
best
to
use
an
R-X
diagram
and
plot
the
line
and
the
relay
characteristics
to
scale
to
check
the
application.
This
has
been
done
in
Fig.
4
for
the
sample
calculations
just
described.
The
various
characteristics
and
points
shown
are
as
follows:
OA
protected
line
DC
=
90
percent
of
protected
line
08
=
150
percent
of
protected
line
OF
=
reach
at
75
degrees
E
=
center of
M 1
characteristic
00
M 2
forward
offset
at
75
degrees
OH
=
M 2
reach
or
diameter
at
75
degrees
0 =
center
of
M 2
characteristic
The
optimum
settings
to
provide
the
narrowest
combined
relay
characteristic
would
be
to
have
equal
diameters
for
M 1
and
M
with the
overlap
kept
to
the
minimum
reconmmended
20
percent.
This
may
not
always
be
practical
or
feasibie
and
a judicious
compromise
may
be
advisable
to
take full
advantage
of
other
fea
tures
such
as
the
first
zone
backup
feature.
ihenever
the
reverse
offset of
the
M 1
first
zone
unit
is
used, the
forward
reach
setting
of
the
M 1
unit
is
undisturbed.
This
offset
is
used in
a
situation
as
described
under
APPLICATION.
Since
the
offset
voltage supplied
by
the
tra9sactor
is
inserted
in
the
M 1
polarizing
circuit
only,
the
forward
reach
of
the
unit
into t’ie
protected
line
remains unchanged.
The
tap
setting
used on
the
target and
seal-in
unit
is
determined
by
the
current
drawn
by
the
trip
coil.
The
0.6
ampere
tap
is
used
with
trip
coils which
operate
on
currents
ranging
from
0.6
amperes
to
2.0
amperes
at
the
minimum
control
voltage
while
the 2.0
amperes
tap
should
be
used
when
trip
currents
are
greater
than
2.0
amperes.
It
is
not
good
practice
to
use
the
0.6
ampere
tap
when
the
trip
current
is
greater
than
2.0
amperes
since
the 0.6
ohm
resistance
of
the
O.
ampere
tap
will
cause
an
unnecessarily
high
voltage
drop
which
will
reduce
the
voltage
of
the
circuit
breaker
trip
coil.
If
the
tripping current
should
exceed
30
amperes,
it
is
recommended
that
an
auxiliary
tripping
relay
be
used.
OPERATING
PRINCIPLES
The
eho
units
of
the
GCYB1
relay
are
all
of the
four
pole
induction
cylinder
construction
in
which
torque
is
produced
by
the
interaction
between
a
oolarizinq
flux
and
fluxes
proportional
to
the
restraining
or
operating
quantities.
The
method
of
obtaining
the
mho
characteristic
for
the
N 1
unit
differs
from
that
used
for
th’
N 2 .
Both
schemes
are
described
below.
N 1
Unit
The
schematic
connections
of
the
M 1
unit are
shnwn
in
Fig.
3.
The
two
side
poles,
enerqized
by
phase—
to-phase
voltage,
produce
the
polarizing
flux. The
flux
froim
the
front
and
rear
poles,
energized
by
the
difference
between
-the
secondary
vol
taqe
of
transactor
TR-l and
a
percentage
of
the
same
phase-to-phase
voltage,
interacts
with
the
polarizing
flux
to produce
torque.
The
torque
equation
can
be
written
as
follows:
9

GEK-26437
Torcue
KE
(IZT1
-
TE)
cos
p
(1)
where
E
= phase—to-phase
voltage
(F 12 )
I
delta current
(‘11
- 12)
ZT 1
= transfer
impedance
of
transactor
TR-l
(design
constant)
p
= angle
between
E and
(1Z 11
- E)
K
= design
constant
T
= auto-transformer
tap
setting
That
this
equation
(1) defines
a
mho characteristic
can be shown
graphically
by
means of Fig.
5.
The
vector
IZT1
at an
angle
9 determines
the
basic minimum
reach of
the
unit
for a particular
tap setting
of the
transactor
TR-l primary.
Assuming
finite
values of
E
and (IZT1
- TE),
the
balance
point,
torque
=
0,
will
occur
where
cos
P
=
0, that
is
where the angle
P
is
90 degrees.
The
locus
of
the terminus
of vector
TE
(point A
in Fig. 5)
which
will
cause the
angle
p
to
always
be
90 degrees
is
a
circle
passing through
the
origin and
with
the
vector
IZT1
as
a
diameter.
Considering
further
the
diagram
in Fig. 4,
we note that
the angle
P
is less
than
90
degrees
for
an
internal
fault (point
C) and
the
net torque
will
be
in
the closing
direction
(cos
p
is positive);
and
that
the
angle
p
is
greater
than 90
degrees for
an
external
fault (point
0) and
the net torque
will
be
in
the
.pning
direction
(cos
P
is negative).
M 2
Unit
The schematic
connections
of the M 2
unit
are shown
in Fig.
3. The two
side
poles, energized
by
phase—
to-phase
voltage,
produce the
polarizing
flux. The
flux in the
front pole,
which
is
energized
by
a
percent
age of
the
same
phase—to-phase
voltage,
interacts with
the
polarizing
flux to produce
restraint
torque.
The
flux
in
the
rear
poTe, which
is energized
by
the
two
line
currents
associated
with
the same
phase-to—phase
voltage,
interacts
with
the
polarizing
flux
to
produce operating torque.
The torque
at the
balance
point of the
unit
can
therefore
be expressed
by
the following
equation:
Torque
0
= El cos
(0
- 9)
-
KE 2
(2)
where:
E
= phase-to—phase
voltage
(F 12 )
I
= delta
current
(11—12)
9 angle
of maximum
torque
of
the
unit
0
= power
factor
angle of fault
impedance
K
= design
constant.
To prove that
equation
(2)
defines
a
mho characteristic
divide both
sides
by
F 2 and
transpose.
The
equation
reduces
to:
3-cos
(0
- 0)
= K
or:
Y cos
(0
- 9)
= K
(3)
Thus,
the
unit will
pick
up at a
constant
component
of admittance
at
a
fixed
angle depending
on
the
angle
of
maximum
torque.
Hence the
name mho
unit.
CHARACTERISTICS
‘ mit
pedance
Characteristic
Th impedance
characteristic
of the unit
is
shown in Fig.
5
for the
0.75
ohm
basic minimun
reach
settinG
at a maxiMum
torque angle of
-75
degrees.
This
characteristic
is
obtained
with
the
terminal
voltage
o
tne relay
supplied
directly
to the restraint
circ.,t of
the
M 1 unit,
that is
with
the M 1
taps on the
ajtc-transforrer
tao
block set
at
100
percent.
This circular
impedance
characteristic
can
be enlarged,
tmit
i
unit
redh
increased,
by up
to
10/1
by reducing
the
percentage
of the
terminal
voltage
supolied
Er the