Choosing High-Power, EMC-Hardened Time Relays for HV Control – Meet ODES STR-F1

TonyZhang
10 hours ago
5 min read

Why HV Primary Control Now Demands “High-Power, EMC-Hardened” Time Relays

In high-voltage circuit breaker control circuits, timing is not just a detail – it is part of the protection and interlocking function itself. But the environment around primary equipment is harsh:

Strong electromagnetic disturbance from switching operations
Inrush and back-EMF from trip/close coils and contactors
Induced voltages on long control cables

Several utilities now explicitly require that time relays used in three-phase disagreement supervision circuits must have:

Pickup (start) power ≥ 5 W, and
Defined high EMC immunity

The goal is simple: the relay must not react to transient interference, and must remain stable when the DC system experiences surges and dips during primary switching.

To address these requirements, ODES has developed the STR-F1 EMC-hardened time relay, designed specifically for:

Three-phase disagreement supervision timing in HV breakers
Energy-storage (spring-charging / hydraulic) timing in operating mechanisms

STR-F1 combines ≥ 5 W pickup power, IEC level-IV EMC performance, and a wide timing range from 0.05 s to 10 h, providing deterministic timing in “strong disturbance + strong inrush” environments. More information on STR-F1 and related products is available at www.odes-electric.com.

Two Core Applications: Disagreement Timing and Energy-Storage Supervision

1. Three-Phase Disagreement Time Control

Three-phase disagreement supervision is used to detect when breaker poles do not reach the same position within a defined time. It is tightly linked to:

Breaker failure logic
Alarm and indication
Interlocking of primary switching operations

In this circuit, a time relay:

Starts when a disagreement condition is detected
Trips or alarms if the condition persists beyond the set delay

Because auxiliary contacts and field wiring can show transient inconsistencies at the moment of operation, this circuit requires high disturbance immunity. A low-power, lightly filtered time relay can be incorrectly triggered by:

Coil inrush effects on the DC bus
Induced transients from nearby switching
Brief contact bounce in auxiliary switches

STR-F1 addresses this by combining:

≥ 5 W pickup power, which raises the energy threshold for operation, and
An internal design tuned to resist AC ripple and DC transient mis-operate conditions

As a result, STR-F1 starts timing only on sustained, valid disagreement inputs, not on micro-disturbances that occur during normal switching.

2. Energy-Storage Circuit Time Control

Energy-storage (spring-charging or hydraulic) circuits drive motors that charge breaker operating mechanisms. A time relay in this path is used to:

Define a maximum charging duration (timeout protection)
Coordinate charging intervals to protect the auxiliary DC supply
Implement simple sequence control across multiple breakers

The challenges here include:

Motor inrush and stall currents creating DC bus disturbances
The need to detect genuine timeout conditions, not momentary dips
Avoiding unnecessary tripping of supply or local protection due to prolonged charging

STR-F1 provides:

Accurate timing from hundreds of milliseconds to several hours
High pickup power to discriminate between real command conditions and transient supply excursions
Robust EMC design so that timing precision and stability are maintained under repeated motor starts and heavy-duty switching

This ensures the mechanism is fully charged when it should be, and that timeouts only occur when there is a genuine mechanical or electrical problem, not because the timer itself reacted to disturbance.

STR-F1 as an EMC-Hardened Time Relay for Primary Circuits

1. High Pickup Power: Standing Up to Inrush and Transients

Trip and close coils and contactors are inductive loads. At switching instants they produce:

Steep inrush currents
High-di/dt and associated transient voltages

If the time relay’s input circuitry is too sensitive, these transients can:

Start timing when no valid command exists
Interrupt timing when a valid command should continue

By designing STR-F1 with pickup power ≥ 5 W, ODES ensures:

The relay requires a clear, sustained energy input to start timing
Short, low-energy disturbances are filtered out at the physical level
The timer logic enters a stable operating state immediately after energisation, reducing the risk of false stop/start cycles when the DC bus is disturbed

In practical terms, this makes STR-F1 suitable for primary control circuits with strong inrush and transient behaviour.

2. EMC Level-IV: Designed for HV Switchyard Conditions

STR-F1 is designed and tested for EMC level-IV conditions typically seen in high-voltage environments, including robust performance under:

Electrostatic discharge (air and contact)
Fast transient bursts on power and output circuits
Surge events in common and differential mode

This EMC “headroom” helps:

Maintain timing accuracy and repeatability in the presence of disturbance
Prevent unintended operation or reset of the timing process
Support use of STR-F1 in AIS, GIS and power plant control cabinets close to primary equipment

The combination of high pickup power and level-IV EMC performance is what differentiates STR-F1 from standard industrial-grade time relays.

3. Wide Timing Range: From Milliseconds to Hours

STR-F1 supports a wide, continuous timing range:

From 0.05 s level
Up to approximately 10 h

With small hysteresis and high repeatability, this allows one device to cover:

Millisecond-class interphase timing in three-phase disagreement supervision
Second-class intervals for energy-storage motor timeout and coordination
Longer supervision windows where process sequences need extended timing

Typical logic behaviour:

On-delay on energisation – timing starts when supply is applied
Immediate reset on de-energisation – timing cancels instantly when the input is removed

This “on-delay, instant return” pattern matches the needs of both disagreement and energy-storage circuits.

Key Technical Parameters

STR-F1 is engineered specifically for primary control environments. Representative parameters include:

Operating mode
Timing range
Control supply (DC grades)
Pickup power
Output contacts
EMC performance
Environmental parameters

These parameters ensure compatibility with high-voltage switchgear and power plant secondary environments, not just office-grade control panels.

Turning HV Timing Problems into a Repeatable Design Pattern

In many projects, “strong disturbance + strong inrush + high consistency” in primary control circuits creates three recurring challenges:

Time relays triggered by disturbance, not real commands
Unstable timing behaviour under DC bus dips and surges
Difficulty reproducing behaviour across bays and stations

By using STR-F1 as a standard high-power, EMC-hardened time relay for:

Three-phase disagreement supervision, and
Energy-storage motor supervision,

designers can convert these challenges into configurable, repeatable timing functions:

Pickup behaviour defined by ≥ 5 W start power
EMC behaviour aligned with level-IV immunity
Timing ranges wide enough to cover both fast coordination and longer mechanism cycles

Instead of bespoke fixes on each project, the time relay becomes a standard component with known behaviour, improving maintainability and fleet-wide consistency.

Conclusion: When the Specification Says “High-Power, EMC-Hardened”, Choose STR-F1

When a high-voltage control scheme explicitly requires high-power, EMC-robust time relays, STR-F1 provides a ready-made answer:

≥ 5 W pickup power designed for coil inrush and transient-rich environments
Level-IV EMC design to maintain timing precision under disturbance
Wide timing range (0.05 s–10 h) for both interphase supervision and energy-storage control
2DPDT 8 A contacts, DC supply grades tailored to substation DC systems, and V-0 industrial enclosure

For engineers facing new specifications on “high-power, EMC-hardened timing startup” in HV primary control, STR-F1 turns that requirement into a practical, standardised solution.

If your HV breaker control or energy-storage circuits now need ≥ 5 W, EMC-hardened time relays, ODES can help you consult on STR-F1 application, request model tables and setting lists, and learn how to standardise high-power time relays across your primary control schemes.