What is lock out relay function why it is needed?Lock out Relay is the Master Trip relay( It is a latch relay once operated we have to reset it by manual) Which is used for Generator protection, Transformer protection, Turbine protection (Fixed in indoor Panel, Standard manufacturer only making those relays) if it operated because of any fault in above the after clearing all the fault we have to reset it by hand(normally available 110Volts or 220Volts DC).Generator lock-out relay The description of an 86 device is a locking-out or lock-out relay. In general, the 86G-1 and 86G-2 relays on the Generator Protection Panel are actuated by one of several generator protection relays-usually, 87 devices (differential current detection devices-and occasionally, others as specified by the owner, insuring agency/company, local regulations, or utility requirements.Sometimes, numerous devices were grouped to actuate 86G-1 OR 86G-2 in order to provide some differentiation as to the exact cause of the trip.When an 86G-n relay is actuated by one or more generator protective relays/devices, the device/relay which actuated the lock-out should have a flag or illuminated indicating light to signify which device/relay detected a serious problem which could cause damage to the generator. When the actuating device is identified, the cause should be investigated and understood BEFORE the unit is re-started.When an 86G-n device is actuated, the generator breaker is opened (tripped), excitation is usually de-energized, and the turbine is usually tripped (emergency shutdown).The 86G-n relays require a manual reset (they must be manually rotated to return to the reset position) in order to permit a turbine re-start-hence the lock-out function.Refer to the Generator Protection Panel elementary drawings for the exact details of what devices actuate the 86G-n relays at your site.86 Lockout relayis an electrically operated hand or electrically reset auxiliary relay that is operated upon the occurrence of abnormal conditions to maintain associated equipment or devices out of service until it is reset.94 Tripping or trip-free relay Functions to trip a circuit breaker, contactor, or equipment, or to permit immediate tripping by other devices; or to prevent immediate reclosing of a circuit interrupter if it should open automatically, even though its closing circuit is maintained closed.What is the difference between the 94 lockout relay and 86 lock out relay ?I have noticed that the 94 lockout relay is activated when the distance relay is activated and 86 is activated when the 87T differential is activated. But why cant the same lockouts be used for both the protection schemes.l 86 lock out relay is hand reset used for mechanical protection (permanent fault) & 94 lockout relay is self reset used for transient fault (temporary fault condition) this is major different between 86 and 96 lockout relay.l 94 lockout relay is for line fault only. 86 lockout relay is master trip relay. It trips both primary and secondary of the transformer as the fault is of serious nature.l 86 lock out relay is an electrically operated hand, or electrically reset relay or device that functions to shut down or hold an equipment out of service, or both, upon the occurrence of abnormal conditions. 94 tripping relay is having function to trip a circuit breaker, contactor or equipment, or to permit immediate tripping by other devices. or to prevent immediate reclosing of a circuit interrupter if it should open automatically even though its closing circuit is maintained closed.l Lockout relay is hand reset relay in this case both the relays are hand reset relay. Only difference is that 94 lockout relay is used for line protection and can also be provided with auto reclosing facility. If the auto reclosing is not successful then in that case 94 goes to Lockout state and shall be manually reset. In case of 86 there is no Auto reclosing feature available. It goes to lockout state directly.l 86 is actually an electrically/Hand reset Master trip relay that trips both the primary & Secondary of a Transformer whereas 94 is a lockout relay that is used in transmission line protection eg. in an Autorecloser. In case of a fault the Autoecloser shall start its O-t-CO-T-CO-T-CO-T-CO operation. After un successfully trying to reclose the line, the 94 Lockout relay shall act after the time duration set & will put the Autorecloser in an Lockout condition so that there are no further reclosing attempts.l 86 Lockout relays are used by many utilities in electrical power transmission substations to trip and hold out of equipment service within a protected zone on the occurrence of protection relay operation which requires inspection and/or repair before the zone may be safely placed back in service. The original intent of lockout was that on operation, maintenance or operating personnel would inspect and repair as required the lock