Vault Transformer Monitoring | Network Transformers

Vault Transformer Monitoring Where It Really Counts

What is a vault transformer?

A vault transformer (or a network transformer) are power transformers located in underground concrete holding areas known as vaults in major cities. There may be multiple transformers found in a single vault. These transformers distribute power and enhance reliability by maintaining a steady flow of power to all customers despite the loss of one or more feeder circuits. Therefore when one vault transformer fails, it can take out the entire vault and even cause serious harm to the public.

City Scape where a vault transformer may be found

Failure Modes of Vault Transformers

Cable Compartment Explosion on a vault transformer

Vault Transformers have three main compartments: cable, switch, and main tank. Failure can happen in any of the compartments but is most likely to occur in the cable compartment.

Vault Transformer Monitoring

Traditional Hydrogen Monitoring

Due to the unique design of network transformers, extant monitoring applications are deficient in their ability to capture the root causes related to the failure of this type of transformer. Despite the high criticality of these transformers and the potential harm catastrophic failure poses to the general public, installation of a multi-gas monitoring system is difficult to justify given the relatively low cost of these transformers. Therefore, the best option to monitor a vault transformer is a hydrogen monitor in conjunction with pressure and thermal sensors, because hydrogen is a useful indicator for early detection of incipient faults.

Traditional hydrogen sensors are used in-oil. But because failure can happen in any of the three compartments, an in-oil hydrogen sensor would need to be installed in each of the three compartment drain valves in order to properly monitor for hydrogen. This approach is problematic because it drives up cost. Many settle for installing one sensor in the main tank but this doesn’t watch the compartment most likely to fail.

Headspace Hydrogen Monitoring

A more cost effective option is monitoring hydrogen in the headspace of the transformer. This option offers a quicker response because hydrogen accumulates in the headspace faster than it takes to dissolve in oil. This approach requires one sensor that samples gas from each of the three compartments and after evaluation, returns it back into the headspace. Watch this video to see how it works.

What should I look for in a vault transformer monitor?

Vault Transformer Hydrogen Sensor
  • Monitors all three compartments
  • Monitors and equalizes pressure between the three compartments
  • Single sensor
  • Monitors hydrogen in the headspace
  • Maintenance free
  • Submersible
  • Easy to install
  • Self calibrating

Introducing the VaultSafe Transformer Monitor

Subsafe Hydrogen Monitor

Dynamic Ratings VaultSafe monitors hydrogen gas and pressure in all transformer compartments which provides early detection of problems and greatly reduces the potential for failure. Pressure is monitored across all three compartments which prevents moisture or atmosphere ingress. The VaultSafe monitor is submersible, maintenance free and self-calibrating.


Additional Resources


Why Monitor Network Transformers?


Preventing Catastrophic Failure of Vault Transformers


An introduction to headspace monitoring for vault transformers.