“Current-Start, Voltage-Hold”: Making DC Anti-Pumping Circuits Actually Reliable

TonyZhang
Jan 8
6 min read

How ODES UEG/I DC current relays distinguish real coil operation from virtual voltage and transient spikes

Why Voltage-Only Logic Is Not Enough in DC Control Circuits

In DC trip and close circuits, engineers face three recurring headaches at the same time:

High inrush current when a trip or close coil is energized
Short-duration DC bus dips and ripple during switching events
Long control cables that pick up induced transients and create “virtual voltage”

If the supervision or anti-pumping logic only looks at voltage, it can easily:

“See” a DC voltage on an open or poorly connected circuit
Miss the fact that the coil never carried current
Misinterpret short-duration bus dips as loss of command and drop out too early

The result: nuisance operation, unreliable blocking, and hard-to-trace intermittent faults in DC control and anti-pumping circuits.

ODES developed the UEG/I DC current relay around a different principle:

Start on current, hold on voltage. Use coil current as the authenticity criterion for operation, and use voltage as the stability criterion for holding.

By doing so, the relay separates real coil energization from virtual voltage and transient spikes, making anti-pumping and DC supervision circuits significantly more robust. More information on related DC relays and auxiliary devices is available at

www.odes-electric.com.

Core Principle: Current-Start, Voltage-Hold

The UEG/I DC current relay applies a two-stage decision process:

Current-start (action authenticity)
Voltage-hold (action stability)

This approach answers two key questions in DC logic:

“Did the coil really operate?” → answered by current-start
“Can I keep the logic latched without reacting to small DC disturbances?” → answered by voltage-hold

Scenario 1 – Breaker Trip / Close Circuits: Filtering Out Empty Voltage and Short Dips

Pain point In breaker control circuits, when a protection output issues a trip or close command, the coil sees:

A millisecond-scale inrush current
A possible short-term DC bus sag or ripple

Traditional supervision that says “voltage present → relay operates” can misbehave:

It may operate with no real coil current, if the circuit is open but still shows DC potential.
It may drop out or chatter during a brief DC bus dip, even though the command is still valid.

UEG/I solution

Start on coil current
Then hold on DC voltage

This makes it ideal in breaker anti-pumping and blocking circuits, where:

You want to confirm that a real trip/close action has occurred, not just that “some voltage exists.”
You want the blocking logic to ride through short DC disturbances without unintended reset.

For more complex anti-pumping schemes, engineers can select:

UEG/I-2H2D – two normally-open (H) and two normally-closed (D) contacts
UEG/I-4H – four normally-open contacts

This allows control, blocking, and alarm signals to be separated into dedicated contact sets, avoiding parallel connections that introduce uncertainty.

Scenario 2 – Long-Distance Trip Circuits: Detecting “Virtual Voltage” and Improving Redundancy

Pain point In traction substations, wind farm step-up substations, and other distributed installations, secondary cables are often very long and sometimes fed from sectionalized DC sources. Poor connections can create “virtual voltage” conditions:

DC voltage can be measured at a point, but
The downstream coil or load does not actually draw current due to an open or high-resistance connection.

This leads to unstable:

Changeover logic
Redundant trip paths
Backup input schemes

UEG/I solution

By installing UEG/I at key points such as DC segmentation nodes or feeder branches:

Start on load current
Hold on local voltage

This behaviour:

Prevents “virtual voltage” from triggering changeover or backup insertion.
Improves the determinism of redundant blocking or trip paths in long DC circuits.

Scenario 3 – Renewables and Rail: Distinguishing Spikes from Real Operations

Pain point In wind power collection systems, photovoltaic combiner and inverter fields, and rail traction substations, secondary circuits are exposed to:

Long cable runs near high-current feeders
Strong electromagnetic fields and common-mode disturbances
Induced transient spikes and surge events

If DC supervision is based purely on voltage sensing, it can be misled by:

Narrow spikes that cross the voltage threshold but do not drive any significant current
Spurious induced voltages in parallel control cables

UEG/I solution

Because the relay’s action criterion is “is there real coil current?”, UEG/I naturally rejects:

Transient spikes that only show voltage but do not sustain current
Short-lived induced voltages without a genuine DC load path

After a valid current-based start, voltage-hold then ensures that:

The output contact remains stable through disturbances,
As long as the DC supply feeding the holding circuit stays above the dropout threshold.

This makes UEG/I particularly suitable for renewable energy and traction applications, where electromagnetic conditions are harsh and DC circuits are long and dispersed.

Engineering Implementation Checklist

To apply “current-start, voltage-hold” logic correctly, engineers should consider four key design points.

1. Use Current-Start for Authenticity, Voltage-Hold for Stability

Current-start ensures that only real load current can initiate an action.
Voltage-hold ensures that once action is validated, the relay output remains stable against small DC variations.

This dual criterion improves both selectivity (true vs. false operations) and stability (no chatter or flicker).

2. Choose the Correct Holding Voltage Pick-Off Point

Take the holding voltage downstream of the command chain or after the relevant series contacts.
This guarantees that when the command is removed or permissive conditions disappear, the relay is reliably de-energised and resets.
A poor choice of holding tap (for example, upstream of key contacts) can leave the relay latched when it should release.

3. Plan Contact Allocation by Function

UEG/I offers multiple contact configurations, for example:

2H2D – two normally-open, two normally-closed
4H – four normally-open
3H1D – three normally-open, one normally-closed

Allocate contacts by function:

One group for anti-pumping or blocking logic
One group for status indication and alarms
One group for interlocking or permissive signals

This reduces the number of parallel connection points and cross-couplings that can complicate logic and trouble-shooting.

4. Integrate with Existing Interposing Relays and Alarm Units

UEG/I is not a replacement for all auxiliary relays; it is a specialised element in the chain:

Combine UEG/I with interposing relays, DC supplies and alarm units to form a closed loop of “action – hold – alarm”.
Use the current-start output to drive interlocks or supervision logic.
Use dedicated contacts for alarm when DC conditions or current flow deviate from expected patterns.

Properly integrated, UEG/I helps simplify schematic diagrams and reduce ambiguous wiring, while improving the observability of DC control circuit behaviour.

Field Application Example

In a ±500 kV DC project in Southwest China, a major retrofit required more secure breaker anti-pumping circuits under strong DC disturbances. UEG/I-2H2D/220 V DC relays were introduced as key components in the anti-pumping path.

Results seen by the secondary-system integrator and the design institute included:

More deterministic blocking behaviour during heavy-duty operations
Clear distinction between real coil energisation and DC bus disturbances
Reduced nuisance events in the disturbance recorder traces during commissioning

The solution has since been recognised as a robust way to upgrade existing anti-pumping schemes without large-scale rewiring.

Conclusion: From Voltage-Only Logic to “Current-Start, Voltage-Hold”

DC control and anti-pumping circuits are no longer simple “on/off” paths. With inrush currents, DC bus disturbances, long cables and harsh EMC environments, voltage-only supervision is not enough.

The UEG/I DC current relay addresses this by:

Starting on current to prove that a real load has been energised
Holding on voltage to ride through expected disturbances while maintaining deterministic dropout
Providing multiple contact configurations (2H2D, 4H, 3H1D) for structured control, blocking and alarm functions

For breaker control, remote trip circuits, renewables and traction, this “current-start, voltage-hold” architecture offers a more reliable foundation for anti-pumping and DC supervision design.

If you are revising anti-pumping circuits or DC control schemes in substations, renewables or traction applications, ODES can help you consult on “current-start, voltage-hold” architectures, request UEG/I terminal maps and sample schematics, and learn how to integrate these relays into existing systems with minimal rewiring.