21-05-2012, 01:26 PM
Transformer differential protection
Transformer differential protection.pdf (Size: 151.73 KB / Downloads: 687)
Application
The RADSB is a protective relay intended for all types of three-phase power transformers. By including additional input restraint modules,
up to 6 transformer windings or restraining inputs can be connected. The relay is also well suited for generator and step-up transformer
overall protection, often including the auxiliary transformer in the protected zone.
Design The RADSB relay is available with two, three, five or six through-current restraint inputs, and can be used for dual-winding or
multi-winding transformers which have one or more circuit-breaker for each winding. The relay is built up of the following modules:
• Test switch, type RTXP 18
• Dc-dc converter, type RXTUG 22H
• Transformer units, type RTQTB 060 and
• Measuring unit, type RXDSB 4
• Tripping relay, type RXMS 1 or RXME 18
• Indicator, type RXSGA 1 or flag indicator
In versions with an indicator, LED’s indicate unrestrained operation and restrained operation and also the phase which caused the latter
operation. In versions with a flag relay, a red flag becomes visible when the differential relay operates. All versions are listed in the
ordering table. The RADSB relay can be connected directly to the main current transformers; however, when this is not practical, interposing CT’s are used for ratio and phase-angle matching purposes. Interposing CT’s provide an additional point of insulation so that different sets
of main CT’s can be earthed independently of each other. In the case of long CT leads, interposing current transformers can be used to
reduce the secondary CT lead burden to the relay (use of 1 A relay is advantageous). When internal faults such as short-circuits between phases, earth faults or inter-turn short-circuits occur, the differential relay rapidly initiates disconnection of the supply to the transformer. On the other hand, the RADSB is stable for differential currents
which are caused by external faults, inrush currents or overvoltages. The operate values for restrained and unrestrained operation are
set with switches on the measuring unit. The operate times of the relay are shown in Fig. 2. RADSB has static measuring circuits with active filters to enable optimum utilization of the harmonics in the differential current while restraining inrush currents and overvoltages. The restraint limits in the case of external faults are shown in Fig. 3
Type SLCE interposing current transformers:
• Type SLCE 12 or 16
(alt. three-phase set with 3 SLCE 12)
• Quantity
• Ordering No. (from Table 7: Interposing
CT selection)
• Desired ratio connected (factory setting)
Mounting:
• RADSB is delivered on apparatus bars.
When additional mounting is required use a 4U equipment frame for 19” rack mounting or a type RHGX 12 or 20 case for panel mounting. For installation and connection material see Accessories (COMBIFLEX connection and installation) and Mounting system sections of the catalogue.