ABB NSD 70D Family Teleprotection Equipment

ABB NSD 70D Family Teleprotection Equipment

Description 

Teleprotection equipment serves to transmit commands produced by protective relays and systems in HVelectrical power systems. In the event of a fault, it makes a decisive contribution to rapidly and selectivelyisolating the faulty line.

The most important characteristics of teleprotection equipment are security, dependability and transmissiontime. Interference on the communication lines must neither be able to simulate a tripping signal when there isno fault (security) nor inadmissible delay a genuine tripping signal (dependability). High security and highdependability coupled with short transmission times and a narrow bandwidth are contradictory requirements.

The transmission of tripping signals via pilot wires or the speech channels of power line carrier equipment iswidely used. The limited bandwidth of such analogue channels constrains the speed of transmission and thenumber of tripping signals per protection channel. Since the advent of digital transmission systems, however,more and higher capacity channels are becoming available. For example, it is now standard practice for ananalogue speech channel on data transmission equipment to be replaced by an interface for digital data witha transmission rate of 2.048MBit/s or 64 kBit/s or 56 kBit/s. Already optical transmission media are often usedto prevent the infuence of electromagnetic disturbances. Modern teleprotection equipment must take fulladvantage of the capabilities of digital channels without sacrificing any of the characteristics which areessential for the transmission of tripping signals.

The data transfer rate of the NSD 70D of 2.048Mbit/s or 64 kBit’s or 56 kBit/s is dictated by the capacity of thedata channel. Interference on a data channel results in a higher bit error rate or even loss of synchronism atthe receiver. In the case of the NSD 70D, the probability of false tripping being caused by transmission errorsin the communications channel is a function of the signal evaluation time in the receiver. Thus for digitalchannels as well, the speed of transmitting tripping signals is limited by the security requirements. Themaximum permissible transmission time depends on the application. For example. permissive transfer trippingprotection schemes require a fast channel with high dependability, but a somewhat reduced security isacceptable. Direct transfer tripping schemes, however, must have the highest possible security anddependability, but have reduced demands on channel speed.

Microprocessor techniques and digital signal processing enable the programmable teleprotection equipmentNSD 70D to be adapted to ideally suit the different operating modes required for tripping signalcommunications equipment.

Features

Versatile application：

Suitable for blocking schemes and permissive and direct transfer tripping schemes via data channels conforming to CCITT G.703 or RS-422/V.11 recommendations or via optical channels.

Programmable：
Programming swtches are provided for setting one of two optional transmission times and the response of the NSD 70D in the event of alarm.

Up to 6 commands per unit：

The NSD 70D is thus able to handle the commands of the phase-by-phase protection scheme for a doublecircuit line

High speed：

Transmission time < 3 ms or < 6 ms at the highest security level

Reliable and robust：

All interfaces and the power supply unit are DC isolated.Duplicate power supply unit can be fitted(redundancy)

Compact：

Two independent units each for 3 commands in one 19″/3U rack or a single unit for up to 6 commands

Digital signal processing：

Reliable operation is assured by a communications protocol and powerful signal evaluation algorithms especially developed for protection applications

T-operation：

Economic scheme for protection lines with multiple terminals (T-ed lines)

Inverse T-operation：

Economic scheme for permissive transfer tripping (overreaching) on T-ed lines

In-operation testing：

Cyclic and manual testing routines enable the integrity of the communications channel to be tested duringnormal operation. The availability of the equipment is continuously monitored by self-testing proceduresInformation on the status and settings of the equipment or alarm signals from the local unit and the unit at theother end of the line can be accessed via a serial interface using a pocket terminal or a PC

Modular structure：

The equipment is logically divided into a signal processing module, a data interface, a relay interface, analarm module, a DC isolated power supply unit and an optional trip counter.

Open system：

With two exceptions, the units of the NSD 70D for digital communication are identical to those of the NSD 70for analogue communication. This high degree of compatibility facilitates the modification of existingequipment and reduces the number of different modules

Addressable：

Assigning addresses to the devices makes it possible to detect for which station a data signal is intended.

Application

The NSD 70D is a digital teleprotection unit capable of transmitting up to 6 tripping signals via a E1(2.048Mbps) digital multiplexer channel, which can be programmed for balanced (120 Ohm) output orunbalanced (75 Ohm) output conforming to CCITT G.703 as well as 64 kBil’s or 56 kBit’s digital multiplexerchannel, which can be equipped with either a contradirectional or a codirectional interface conforming toCCITT G.703, with an RS-422V.11 interface or with an optical interface. For the G.703 64 kBit/s interface tooperate codirectionally, the multiplexer must operate in a plesiochronous mode, because terminal equipmentand multiplexer each have their own clock oscillators with “slightly differing” frequencies (discrepancy < 100ppm). The slip this causes is compensated by periodically omitting an octet or repeating one. How often these”pattern slips” occur depends on the difference in the dock frequencies of the terminal equipment (NSD 70D)and the multiplexer. The ability to program the balanced (120 Ohm) and unbalanced (75 Ohm) integrated inthe E1 interface module, or contra and codirectional interfaces and their integration in PCM interface module,or using the RS-422NV.11 interface or the optical interface permits the NSD 70D to be easily adapted to themultiplexer’s existing interface.

The NSD 70D can be used in blocking schemes, permissive and direct transfer tripping schemes and for the continuous transmission of commands in point-to-point or teed feeder systems. In all cases the hardware is the same.

The equipment is extremely simple to set and to operate, the parameters being set on programming switches.

The basic version of the NSD 70D is intended for the transmission of one command. By inserting further relayinterface modules, it can be expanded for up to six independent commands. With the maximum complementof six commands, one NSD 70D is sufficient for the phase-discriminative protection of a double circuit line.

The unblocking function, which closes an enabling contact for 200 ms in the event of loss of signal, isstandard equipment on all units. This is of consequence mainly for permissive overreaching transfer trippingschemes.

All interfaces are DC isolated. The transmitter signal is activated by applying a DC signal at station batteryvoltage. The receiver is equipped with main and auxiliary contacts for each command output and a common
alarm contact. A trip counter is optionally available.

Stock part list:

G3HF HENF331051R0009
G3HC HENF327935R0005
G3HE HENF327998R0003
G3HM HENF331048R0005
G3HP HENF331132R0021
G3HH HENF327954R0001
G7BGA HENF105334R0010