Static Distance Relay LZ96

Application .1 The distance rely type LZ96 is designed for the high- speed, selective protection of h.v. and e.h.v. networks with effectively earthed neutral. The distance relay can detect all kinds of short circuit and can be used to protect either overhead lines or cables. Owing to its very short tripping time and very high accuracy, it is ideal for .use in networks with high short circuit power and critical stability conditions The distance rely LZ96 is a member of the ‘Modures’ family of BBC rely and is noteworthy for its highly flexible, modular design. As a result of this, the relay can be optimally matched to the line in question and the operating condition. With additional measuring and starting ancillaries it is also possible to allow for extraordinary network conditions. All the usual methods of transfer tripping by a signal link are possible. For auto- reclosure the devices WT91/92 and 96 can be supplied .furthermore, for critical stability conditions in the network protection .against power swings UP91 can be provided The technical details of the rely can be found in the publication CH-ES 65-96, while .its mode of operation is described in publication CH-ES 25-96 Design .2 The relay is housed in standardized 19-inch racks and its design conforms to the modular arrangement of the BBC modures system, as described in publication CH.ES 65-00 The inserts belonging to the relay can be plugged in to the racks. They have standard height of 3.5 unit (1 unit = 44.45 mm). A 19” rack can accommodate up to 24 divisions. The dimensions can be found in the drawing in publication CH-ES 66.80 The basic unit including its d.c./d.c. convertor NF93 is housed in tow racks. A summary of the inserts forming a basic set of distance protection equipment is given in appendix 1. For optional ancillaries, such as reclosing device, power swing protection, etc., there is sufficient space in a third rack.( for summary of the various ancillaries) The racks are ready wired in the factory as a complete assembly. They can be mounted in suitable enclosures with terminals at the front or rear, for flush or surface mounting in or on switchboards. The relay can also be mounted direct in a cabinet. The group of racks is then supplied with cables, to the ends of which .terminal blocks are fitted

Determining the settings 

Within the scope of the present description it is only possible to give basic rules for ,determining the setting .when complicated network conditions are involved Special aspects have to be borne in mind. It is advisable to enter the network data required and the setting to be calculated according to the next sub- chapter in the .table of setting (appendix SK-HESG 2583) :General remarks .The impedance of the primary steps should be taken from the grading plan · .The impedance ratio rz is derived from the data of the instrument transformers · Secondary step impedance and pick- up impedance are derived from the primary · .values by dividing by rz The primary pick –up impedance of the under-impedance starting relay is · .calculated according to the rules given in chapter 3.1 The neutral-current relay is normally set to 0.4 IN in the current unit IL91. The · .pick-up values can be changed to 0.15 IN if desired