2TJM Relay is available in three versions viz. 2TJM 10, 11 and 12. These are disc-operated relays, and provide IDMT, single/three pole, overcurrent protection, with/without highset and with/without directional and phase fault protection. The 2TJM relays are completely drawout, and have 2NO contacts for external tripping purposes.
The relay comprises a die-cast frame, which carries all the sub-assemblies of induction disc, electro-magnetic system, operating coil, plug bridge and the contact assembly. Instantaneous highset and directional elements can be provided.
The electro-magnetic system comprises primary and secondary magnets arranged with four air gaps each contributing to the driving torque. The primary coil energises the primary magnet and a secondary winding which in turn energises the secondary magnet. Tappings on the primary coil permit various fault settings to be made via a plug-bridge. The plug-bridge automatically selects the highest setting when the setting-plug is withdrawn.
Two normally open contacts are provided of the bridging type, the operating arm being driven by a cam track at the hub of the induction disc. This gives considerable mechanical advantage and ensures high contact pressures, even at low operating current levels, making the contacts suitable for direct tripping.
Relay operating time is determined by the starting position of the induction disc, this is set by the time multiplier dial calibrated from 0.1 to 1.0, there is also a ^T^ mark, before the 0.1 setting, in this position the contacts are held closed, locked out. Settings are applied in ampere.
The type 2TJM11 relay is basically similar to the type 2TJM10, the exception being the addition of a miniature instantaneous high-set overcurrent element (type MCAA) which is fitted to the movement frame and has its operating coil connected in series with the relay primary coil. The element is of the attracted armature type and primarily designed for use with I.D.M.T.L. relays. The overcurrent setting is continuously variable by means of the calibrated cam. This element may be ^locked out^ by advancing the setting adjuster to its extremity, i.e. past the highest fault setting. The flag indicator shows on operation and is hand reset by a push fitted in the relay cover.
This relay comprises the I.D.M.T.L. element previously described and a directional element type ^ES^. The elements are vertically mounted on a mild steel back-plate with the directional element in the upper position; the composite relay is then housed in a 11/2 pole vertical case.
The directional element operates on the induction wattmeter principle and consists essentially of an aluminium sector mounted on a vertical spindle and arranged to rotate in the air gap between the magnetic fields derived from the line current and voltage transformers. The electro magnetic system with the three coils which provide loss of voltage compensation and hence reliable operation should the line voltage be reduced, under fault conditions, to values as low as 2% of nominal.
Under healthy system conditions or under fault conditions where the current flow is in the normal direction eddy currents induced in the sector produce a torque, the direction of which restrains relay operation. Should current reversal occur, then the direction of the torque reverses causing the moving system to rotate and thus close the contacts, the latter being so connected that they complete the I.D.M.T.L. element operating coil circuit.
The maximum torque exerted on the movement occurs when the voltage and current in the coils are in phase. However, as the system power factor may be considerably removed from unity under fault conditions, depending on both the nature of the fault and system conditions, the element can be supplied with a phase-angle introduced by fault conditions. This is achieved by employing a suitable shading ring, the requisite value of resistance and the appropriate connection.
45 degree Lead Power Factor Characteristic: Relays supplied with the 45 degree lead power factor characteristic utilise the 90 degree connection, i.e.relays monitoring A-phase current are polarised by B-C voltage, thus the relay develops maximum torque with a 45 degree lagging fault current.
Earth-fault relays are normally supplied with 12 and half degree lagging power factor characteristic. The current coil is connected in the residual circuit of the line current transformers and the voltage coil in the open delta tertiary winding of the line voltage transformer, the voltage coil being suitable for 190V and 63.5V on resistance and solidly earthed systems respectively.
Directional earth fault relays with a 45 lagging power factor characteristics are used in highly inductive earthing systems. The characteristic is achieved in the relay with a RC circuit in the ES element.