numerical current differential protection relay block 7SD600

Features and technical specifications:

1. Local and remote current
2. Differential current
3. Restraint current
4. Via personal computer and DIGSI 3
5. Via RS232↔RS485 converter
6. With modem
7. With substation control system via IEC 60870-5-103 protocol
8. 2 kV isolated RS485 interface, bus connection possible

The following functions are available

1. Current differential protection with external summation current transformer 4AM49 (87L)
2. Suitable for use for distances of approx. 12 km max. via two pilot wires (1200 Ω loop resistance)
3. Differential protection can be combined with an overcurrent release
4. Pilot-wire monitoring function
5. Bidirectional remote tripping
6. Circuit-breaker intertripping at the remote station
7. Seal-in of the TRIP command until manual reset (Lockout function)
8. Minimal current transformer requirements due to integrated saturation detector
9. Restraint against inrush/undelayed trip for high differential fault currents
10. Emergency over current protection

This numerical current differential protection relay block is easily insert in your schematic diagram and connect as you like way.

Application :-

The 7SD60 relay is a numerical current differential protection relay, simple to set, and is operated in conjunction with the remote station via a two pilot-wire link. It is connected to the primary current transformers via an external summation current transformer. The unit operates internally on the summated current taken from the secondary side of the summation current transformer. The link to the remote station
is realized by means of a pair of symmetrical pilot wires allowing distances of up to approximately 12 km. Adaptation to the pilotwire
resistance is effected by means of software within the unit. Therefore, matching is not necessary. The primary fi eld of application of the unit is protection of short overhead lines and cables with two line ends. However, transformers and reactors may be located within the protection
zone. The unit can be fi tted with inrush restraint in such cases. A differential protection instantaneous tripping stage is also provided in this case. Vector group adaptation is not effected inside the unit and must, if necessary, be effected by means of a matching current transformer.
The 7SD60 can be fi tted with a pilot-wire monitoring function. In addition to monitoring the pilot-wire link to the remote station, this also includes bidirectional circuit-breaker intertripping and a remote tripping command. If the differential protection becomes inactive due to a pilot-wire failure, the relay has an emergency overcurrent function as an option. It includes one defi nite-time overcurrent stage and can
be delayed. This unit substitutes the 7SD24 steady-state differential protection. However, direct interoperation with the 7SD24 is not
possible. On replacement of a 7SD24, its external summation current transformer can be used as the input transformer for the 7SD60.

Construction :-

The compact 7SD60 protection relay contains all the components for:
• Measured-value acquisition and evaluation
• Operation and LCD indications
• Alarm and command contacts
• Input and evaluation of binary signals
• Data transmission via the RS485 bus interface to DIGSI or a substation control system
• Auxiliary voltage supply
The primary current transformers are connected to the 4AM49 summation current transformer. At the rated current value of either 1 A or 5 A, the latter outputs a current of 20 mA which is measured by the 7SD60 unit. The summation current transformer is supplied together with the protection unit, if so ordered. The unit can be supplied in two different housings. The one for flush mounting in a panel or cubicle has connection terminals at the rear. The version for panel surface mounting is supplied with terminals accessible from the front. Alternatively, the unit can be supplied with two-tier terminals arranged above and below the unit.

1. Emergency overcurrent protection :-
   If the differential protection becomes inactive due to a pilot-wire failure or an internal or external blocking of the differential function,
   the relay offers a single-stage, defi nite-time overcurrent function. It works with the local fl owing operational current IM1. The pickup value and the delay time are settable via parameters in the device.
2. Overcurrent release / differential current monitoring :-
   The differential protection function can be combined with an additional overcurrent release. To this end, the criteria “overcurrent”
   and “differential current” are linked logically so that a TRIP command is given out by the differential function only when a differential current and an overcurrent coexist. By this means it is often possible to avoid malfunctioning due to pilot-wire short-circuit or wire-break of a connection between a current transformer and the summation current transformer. For this purpose, the 7SD60 is fi tted with an additional differential current monitoring function, which can effectively block the differential protection after a delay of some seconds on reaching of an adjustable value of differential current in conjunction with simultaneous operational current IM1 within the load range.
3. Saturation detector :-
   Improved stability on single-ended saturation of the primary current transformers is ensured by means of an integrated saturation
   detector. It provides additional stability during external faults. 5 ms are enough time to measure an external fault due to a high restraint and small differential current. Indication is done within the additional restraint area (see Fig. 7/4). If – due to CT saturation – the differential current flows into the trip area, the differential trip is blocked for a certain time. Transient saturation of current transformers caused by decaying DC components in the short-circuit current can thus be recognized. As a result, the requirements on the current transformers are reduced so that they are only required to conduct the steadystate through-fl owing short-circuit current without saturation.