GE Vernova MMLG/MMLB Test Blocks and Test Plugs

GE Vernova MMLG/MMLB Test Blocks and Test Plugs

Product Overview

The MMLG/MMLB series test blocks and plugs are products of Grid Solutions under GE Vernova, belonging to the Midos family. Their core purpose is to provide monitoring and secondary injection testing functions for various power system protection schemes, and they need to be used in conjunction with MMLG test blocks and MMLB 01 multi pin test plugs. The product was officially launched in 1983 and has mature market applications. So far, over 500000 MMLG test blocks and over 70000 MMLB 01 test plugs have been delivered; In 2001, GE launched the MiCOM P990 series test block as an alternative to this series, which features automatic internal CT short circuiting function and complements MMLG.

Product model and core specifications

The MMLG/MMLB series includes 4 MMLG test blocks and 1 MMLB 01 test plug, with clear positioning and core features for each model, as shown in the table below:

table

Product Model Product Type Core Positioning/Features Key Specifications

MMLG 01 test block standard version, basic universal 14 circuit, automatic disconnection of 13/14 terminal circuit when the cover is removed, with CT short circuit link

MMLG 02 test block special version, compatible with busbar protection scheme for 14 circuits, 13/14 terminal contacts are normally closed, without cover removal and power-off function

MMLG 03 test block horizontal version, MMLG 01 horizontal version with the same core functions as MMLG 01, installation form is horizontal

MMLG 04 test block horizontal version, MMLG 02 horizontal version with the same core functions as MMLG 02, installation form is horizontal

MMLB 01 test plug multi pin version, compatible with all MMLG to use 28 4mm sockets, with socket numbers corresponding to the test block terminals one by one

Core structure and working principle

MMLG test block

Core structure: Equipped with 14 circuits, each circuit contains a pair of normally closed internal contacts. During normal operation, the contacts close to complete the circuit connection; Each circuit is led to an independent terminal pair at the back of the test block, and external devices (CT, VT, DC power supply) need to be connected to odd numbered terminals.

Safety structure: When the shell cover is in place, it provides anti electric shock protection. Removing the front cover will expose an orange identification strip, which intuitively indicates that the system is in a non working state; The metal probe on the inside of the front cover of MMLG 01 automatically retracts when the cover is removed, disconnecting the circuit between terminals 13/14. If the DC auxiliary power supply is connected to this circuit, it can prevent the protection system from tripping incorrectly during testing (MMLG 02 does not have this function).

Size specifications: Belonging to Midos System No.2 specification, it adopts panel embedded installation, and the specific installation opening size has clear standards (such as panel opening key dimensions including 4.40mm, 168mm, 212mm, etc.).

MMLB 01 test plug

Core matching: When inserting the MMLG test block, its internal normally closed contacts will be disconnected to achieve circuit isolation, and testing can be carried out without changing the original wiring of the protection system.

Socket zoning: The white half socket corresponds to the isolated relay circuit, and the orange half socket corresponds to the potential live power circuit. Testing equipment can be connected to the corresponding area to complete monitoring/testing.

Physical fixation: It can be firmly inserted and fixed into the test socket of the MMLG test block through two rolling screws, and all 28 sockets are compatible with 4mm telescopic sheath test cables.

Core working logic: During normal operation, the internal contacts of MMLG are closed, and the protection system circuit is connected; During testing, insert MMLB 01 and disconnect the contacts to achieve circuit isolation. Connect the testing equipment through a plug socket to complete monitoring, secondary injection testing, and other operations. After the test is completed and the plug is removed, the MMLG contacts automatically close, restoring normal system operation.

Installation and accessory requirements

Installation of MMLG test block

Terminal configuration: Each terminal is equipped with a 4mm screw interface (compatible with L-type pre insulated crimping terminals) and 2 4.8mm × 0.8mm inserts (compatible with BS5057 standard snap on connectors).

Grounding requirements: The protective grounding terminal at the rear of the test block must be connected to a minimum 2.5mm ² wire; If a circular terminal block is used to connect the rear terminal block, an insulation crimping type should be used to maintain the design insulation level.

Installation adaptation: It can directly install relays and systems close to the height of a 4U rack, and adapt to the layout of power system cabinets.

MMLB 01 Test Plug Accessories

Standard accessories: Each MMLB 01 comes with 6 short-circuit plug links, each link consisting of two 4mm stackable telescopic sheath plugs and a 150mm cable.

Customized accessories: 2m testing cables of the same specifications can be customized according to requirements for connecting testing equipment, which requires separate application.

Core advantages of the product

Installation convenience: Suitable for power protection equipment with a height of 4U rack, it can be installed nearby without additional planning of installation space, and conforms to the standardized design of power system cabinets.

Efficient operation: During testing, there is no need to remove or modify the original wiring of the protection system. Simply plug in the test plug to achieve circuit isolation, greatly simplifying the operation process of monitoring, isolation, and secondary injection testing, and improving testing efficiency.

Safety protection

Adopting a 4mm stackable telescopic sheath plug to achieve enhanced finger safety protection and prevent electric shock during operation.

MMLG 01 has the function of removing the cover to cut off power, avoiding the risk of false tripping during testing from the source; The orange identification bar provides a visual warning of the working status.

The test plug is designed with live/isolated zones, clearly distinguishing the test circuit and reducing safety hazards caused by wiring errors.

Strict safety operation standards

There is a potential risk of electric shock during testing operations, and the following core safety requirements must be followed, and only qualified professionals are allowed to operate the equipment:

CT secondary protection: Before inserting MMLB 01, the socket corresponding to the secondary winding of the current transformer (CT) on MMLB must be short circuited with an external short-circuit link. It is strictly prohibited to disconnect the secondary circuit of the live CT (which may generate fatal high voltage and damage the insulation); The MMLG series does not have an internal CT short-circuit function, and the short-circuit operation needs to be manually completed by the user.

Power control: When inserting/unplugging MMLB into/from MMLG, all test power sources connected to MMLB must be disconnected first; Temporarily disconnect the secondary circuit of the substation connected to MMLG as much as possible before operation, and if necessary, temporarily shut down the primary system to ensure that no primary current supplies power to the CT secondary circuit.

Accessory inspection: Before use, it is necessary to check the continuity and insulation status of the short-circuit plug/wire link, and visually inspect whether the insulation layer of the test fly wire is damaged; All test lines and short-circuit links must be sheathed.

Wiring verification: The actual wiring of MMLG must be confirmed through necessary measures, and cannot rely solely on the substation circuit diagram; If the on-site conditions are safe, it is recommended to conduct a physical inspection of the actual wiring.

Emergency response: If there are any doubts about the safety operation process, immediately stop all operations.