HD Electric LB-5 Load Box

The HD Electric LB-5 Load Box can be used to apply a resistive load to lightly loaded or unloaded three-phase power systems in order to prevent ferroresonance and subsequently prevent damage caused by this phenomenon.

Ferroresonance occurs most readily in medium voltage distribution transformers and power cables. It commonly occurs during single phase switching. Ferroresonance can result in overvoltage and overcurrent which can cause the breakdown of insulation, subsequently damaging transformers, capacitors and lightning arrestors; it also poses a danger to personnel.

Ferroresonance usually occurs when unloaded three-phase transformers are connected or disconnected one phase at a time. This practice is usual when manually operating cutouts, overhead single-phase switches or underground load break elbows. If there is little or no resistive load during switching this can cause ferroresonance and, if left unchecked, overvoltage can cause connected components to breakdown.

To avoid this eventuality, it is necessary to apply a portable resistive load of at least 5% of the transformer’s full load rating to all three phases. This load is only applied during switching: between the time the first phase and last phase are connected or disconnected. The HD Electric LB-5 Load Box can be used to apply these loads.

The HD Electric LB-5 Load Box provides a resistive load of up to 5kW per phase, a total of 15kW over all three phases. It is always connected to the transformer prior to switching.

When using the HD Electric LB-5 Load Box during the disconnection of an energised transformer, the HD Electric LB-5 Load Box is connected to the live secondary connections. Energisation of the resistive load in all three phases is facilitated by the HD Electric LB-5 Load Box’s three-phase switch; this makes the transformer ready for disconnection.

During the connection of a transformer, the HD Electric LB-5 Load Box is connected to the deenergised secondary transformer connections. It starts up and applies the required load to each successive phase as the transformer is energised one phase at a time.

The HD Electric LB-5 Load Box will automatically switch the load to the applied voltage. It can be used on Y or Δ connected transformers and is rated for secondary voltages of 120/208 and 277/480 VAC. The HD Electric LB-5 Load Box has an operating frequency of 50/60 Hz. The HD Electric LB-5 Load Box is a dual voltage instrument with an auto voltage selection.

Finally, the HD Electric LB-5 Load Box features a portable, on-person design with resistors organised in a Y-formation, the centre of which is connected to the ground lead. It is fan cooled as well as fused protected and will alert the user to a blown fuse via an indication lamp

The HD Electric LB-5 Load Box provides a solution to preventing damage caused by ferroresonance during the connection and disconnection of three-phase transformers.

HD Electric LB-5 Load Box Key Features

• Apply resistive load to lightly loaded or unloaded three-phase power systems in order to prevent ferroresonance 
• Prevent damage caused by ferroresonance
• Apply a resistive load of 5kW per phase
• A total of 15kW across all three phases
• Connect to the transformer prior to switching
• Connect to live secondary connections when disconnecting an energised transformer
• Three-phase switch facilitates the energisation of resistive load in all three phases, making the transformer ready for disconnection
• Connect to the deenergised secondary transformer connections during the energisation of a transformer
• As the transformer is energised phase by phase, the load box will start up and apply the required load to each successive phase
• Automatically switches the load to the applied voltage
• Can be used on Y or Δ connected transformers
• Rated for secondary voltages of 120/208 and 277/480 VAC
• Operating frequency: 50/60 Hz
• Dual voltage instrument with an auto voltage selection
• Fan cooled
• Fuse protected
• Blown fuse indication lamp
• Portable, one-person design
• Resistors organised in a Y-formation with the centre connected to the ground lead
• Provides a solution to preventing damage caused by ferroresonance during the connection and disconnection of three-phase transformers

What’s Included?

• HD Electric LB-5 Load Box