ABB Distribution Protection Unit 1500R
1-7
Protective Functions
9/99
website:www.abb.com/papd
Ground Instantaneous Overcurrent Element 50N-3 (IN>>3) - Level 3, High set
The 50N-3 function operates when the level of ground current exceeds the pickup level. 50N-3 is typically used to
establish high set instantaneous overcurrent protection. If the fault current exceeds the 50N-3 setting a typical scenario
would be to lockout reclosing or operate an external
lockout relay. To operate an external lockout relay
with the 50N-3 only, a programmable output contact
must be mapped to operate on the 50N-3 element
only. This function can also be used as a level
detector supervised by some other function such
as the 32N. See the “Programmable I/O” Section
for more details. The pickup level of 50N-3 is set
as a multiple of the 51N pickup (see Table 1-2). The
timing of the 50N-3 is not selectable and trips
instantaneously with no intentional time delay. The 50N-3 pickup is set in the Primary, Alternate 1, and Alternate 2
settings groups. For the 50N-3 element to operate the “Trip” contact, it must be selected in the “Master Trip Output”
mapping (see “Programmable Master Trip Contact” later in this section). 50N-3 is set by factory default to operate the
“Trip” contact. 50N-3 tripping can be enabled or disabled in each step of the reclose sequence. See “Reclosing” later in
this section for more details.
Negative Sequence Time Overcurrent Element 46 (Insc>)
The negative sequence overcurrent element is used where increased sensitivity for phase to phase faults is desired. In
addition to the typical application of feeder protection, this element can also be applied on DPU1500R relays protecting
a main bus breaker in medium to large distribution substations. The main DPU1500R would typically be set to provide
tripping for bus faults and backup tripping for a failed feeder relay or breaker. In the case of a medium to larger
substation the time and instantaneous overcurrent elements in the main DPU1500R must be set well above the
combined full load current of all the individual feeders. This slows the response to bus faults and decreases the
sensitivity to faults on a single distribution feeder. Since the negative sequence element only looks at the amount of
negative sequence current in the system it can be set just above the maximum negative sequence current level
produced by single phase load unbalance. This makes the main DPU1500R much more sensitive to phase to phase
faults.
Multiple time curves and time dials are available (see Table 1-10) to coordinate with other devices in the system. The
time-current curves included in the DPU1500R are located later in Section 1. User programmable curves and special
Recloser curves are also available depending on the DPU1500R model ordered (see Section 10 for programmable
curves). See Section 12 for help defining the unit model number. The 46 pickup, curve type, and time dial are all set
in the Primary, Alternate 1, and Alternate 2 settings groups. For the 46 element to operate the “Trip” contact, it must be
selected in the “Master Trip Output” mapping (see “Programmable Master Trip Contact” later in this section). The 46
element is set by factory default to operate the “Trip” contact. The 46 element will always initiate reclosing unless the
recloser is disabled. See “Reclosing” later in this section for more details.
There are two selectable reset modes available for the 46 element. The instantaneous mode is used to coordinate with
other instantaneous reset devices such as solid state or microprocessor based relays. In the instantaneous mode the
46 will reset when the current drops below the pickup setting for one half cycle. The delayed mode simulates the action
of an electromechanical induction disk relay. In this mode the 46 reset follows a slow reset characteristic that depends
upon the duration of the overcurrent condition and the amount of load current flowing after the event. The reset time
equations are available at the end of Section 1. When the DPU1500R “Multiple Device Trip Mode” (see “Multiple Device
Trip Mode” in Section 2) is enabled the 46 reset characteristic defaults to the instantaneous mode and cannot be set
to delayed. The reset mode when set applies to all time overcurrent elements in the DPU1500R.
50N-3 Parameter
Range/Curve
Increment
Pickup
0.5 to 20 x 51N setting
0.1x
The 50N-3 element is disabled in the factory default settings.
Table 1-9. 50N-3 (IN>>3) Characteristics
