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I.B. 17555C
Effective November 1999
Page 6
SECTION 2: FUNCTIONAL DESCRIPTION
2-1
PROTECTION, TESTING AND
COMMUNICATION CAPABILITIES
2-1.1 RMS SENSING
Digitrip 3000 Protective Relays provide true RMS sensing
for proper correlation with the thermal characteristics of
conductors and equipment. The root mean square (rms)
value is determined by a microprocessor calculation of
discrete sampled points of the current waveform. This
root mean square value is used for the protection
response and metering displays of the relay.
2-1.2 PICKUP SETTING
A Digitrip 3000 Protective Relay pickup setting is a dis-
crete, preselected value of current used to initiate a trip-
ping action. The Digitrip 3000 has several current based
tripping functions:
• Phase inverse time overcurrent tripping - Thermal,
ANSI, and IEC Curves.
• Ground inverse time overcurrent tripping - Thermal,
ANSI, and IEC Curves. Ground selection is indepen-
dent of phase selection.
• Phase and ground short delay tripping.
• Phase and ground instantaneous tripping.
As shown in Figure 3-1, the ANSI and IEC “Curve
Shapes” are in terms of multiples of I
pu
(Pickup
Current of the CT Primary), whereas ‘short delay”
and “instantaneous” are in terms of multiples of I
n
(5A secondary of CT primary current). The thermal
curve is represented in terms of multiples of I
n
for its
curve shape, short delay, and instantaneous
settings. This must be considered in the coordination
study and in the programming of the Digitrip 3000
Protective Relay.
Example: Thermal Curves, Short Delay and Instanta-
neous settings using I
n
CT Rating = I
n
= 1200A.
Pickup Setting= 1.5
Pickup (amps)= (1 200)(1 .5)
= 1800A.
Example: ANSI and lEC curves using I
pu
CT Rating = 1200A.
I
pu
= Pickup Current = 1800A.
CT Ratio = 1200:5 (Entered as “1200”)
Actual secondary current at pickup =
7.5A = (1800/1200) x 5
2-1.3 TIME SETTING
A Digitrip 3000 Protective Relay time setting is a prese-
lected time delay initiated when a pickup point on the
long or short curve is exceeded. If the current value
drops below the pickup value, the timing function resets.
No memory is provided. If the current value does not
drop below pickup, the amount of delay before tripping
occurs is a function of the current magnitude and the time
setting. The delay can be determined from the appropri-
ate time-current curves.
2-1.4 PROTECTION CURVE SETTINGS
Curve Selection: Extensive flexibility on inverse time
overcurrent (phase and ground) curve shaping is possi-
ble with eleven available curve types. The selection and
associated result is determined by the type of curve
shape that best fits the coordination requirements (Figure
1-4, Table 2.1). Different curve shape settings can be
applied to phase and ground to maximize coordination
flexibility. The curves are discussed in more detail in
Paragraph 3-3.1.
Phase Inverse Time Overcurrent Pickup: The available
pickup settings, shown in Table 2.2, range from 0.20 to
2.2 times (I
n
).
TABLE 2.1 CURVE SELECTION
Curve Type
Selection
Result
Thermal
It
I
2
t
I
4
t
FLAT
Moderately Inverse
Inverse
Extremely Inverse
Definite or Fixed Time
ANSI
MOD
VERY
XTRM
Moderately Inverse
Very Inverse
Extremely Inverse
lEC
lEC-A
lEC-B
lEC-C
IEC-D
Moderately Inverse
Very Inverse
Extremely Inverse
Definite Time
Summary of Contents for Cutler-Hammer Digitrip 3000
Page 18: ...I B 17555C Effective November 1999 Page 12 Fig 2 1 Typical Communications Wiring Diagram...
Page 27: ...I B 17555C Effective November 1999 Page 21 Fig 3 1 Digitrip 3000 Typical Wiring Diagram...
Page 36: ...I B 17555C Effective November 1999 Page 30 Fig 3 11 Local Programming Sequence Flow Chart...
Page 37: ...I B 17555C Effective November 1999 Page 31...
Page 52: ...I B 17555C Effective November 1999 Page 46 Fig 7 5 Short Delay Phase Curves SC 5394 92B...
Page 54: ...I B 17555C Effective November 1999 Page 48 Fig 7 7 Instantaneous Curves SC 5396 92B...
Page 59: ...I B 17555C Effective November 1999 Page 53 Fig 7 12 Short Delay Ground Curves SC 5403 92B...
Page 60: ...I B 17555C Effective November 1999 Page 54 Fig 7 13 ANSI Moderately Inverse Curves SC 6685 96...
Page 61: ...I B 17555C Effective November 1999 Page 55 Fig 7 14 ANSI Very Inverse Curves SC 6686 96...
Page 62: ...I B 17555C Effective November 1999 Page 56 Fig 7 15 ANSI Extremely Inverse Curves SC 6687 96...
Page 63: ...I B 17555C Effective November 1999 Page 57 Fig 7 16 IEC A Moderately Inverse Curves SC 6688 96...
Page 64: ...I B 17555C Effective November 1999 Page 58 Fig 7 17 IEC B Very Inverse Curves SC 6689 96...
Page 65: ...I B 17555C Effective November 1999 Page 59 Fig 7 18 IEC C Extremely Inverse Curves SC 6690 96...
Page 66: ...I B 17555C Effective November 1999 Page 60 Fig 7 19 IEC D Flat Curves SC 6691 96...
Page 68: ...I B 17555C Effective November 1999 Page 62...
Page 73: ...I B 17555C Effective November 1999 Page A5 Fig A 7 DT3001 Typical Wiring Diagram...
Page 76: ...I B 17555C Effective November 1999 Page A8...
Page 81: ...I B 17555C Effective November 1999 Page B5 Fig B 2 Digitrip 3010 3020 Dimensions Inches...
Page 83: ...I B 17555C Effective November 1999 Page B7 Fig B 3 Digitrip 3010 3020 Typical Wiring Diagram...
Page 89: ...I B 17555C Effective November 1999 Page B13...
Page 90: ...I B 17555C Effective November 1999 Page B14...