[Technical Discussion] Hydraulic Electromagnetic Circuit Breaker

Latest update time：2024-06-25

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This chapter introduces hydraulic electromagnetic circuit breakers from the perspective of product structure, working principle, characteristics, advantages and disadvantages. As a less popular product in the circuit breaker category, it can be used as an overcurrent protection solution for high-reliability applications due to its overcurrent characteristics that are not affected by temperature and its high-precision protection characteristics with low overload.

Hydraulic magnetic circuit breaker (HM breaker for short) integrates overload and fault circuit breaker protection functions in a single structure, replacing the overload and circuit breaker protection functions of traditional circuit breakers with thermal and electromagnetic mechanical structures separated. It is very suitable for overcurrent protection of rail transportation, ships, data centers and semiconductor equipment.

Hydraulic electromagnetic circuit breaker cross section

Overcurrent sensor: coil, delay tube, bracket and armature
Operating mechanism: operating handle, release device, contact arm
Arc chamber: arcing horn, arc roller, iron grid pile, fixed terminal

Basic Working Principle

Hydraulic electromagnetic circuit breakers do not have bimetallic strips as low-overload triggers. Instead, they use a coil wrapped around a cylinder connected in series in the main circuit. The cylinder contains an iron core, a spring, and liquid oil. The magnetic field strength is proportional to the current flowing through the coil.

When the current flowing through the coil is less than the rated current, the center iron core squeezes the spring inward, the air gap decreases, and the magnetic field strength increases. At this time, the spring force is greater than the magnetic force, and the armature fails to close.
When the loop current exceeds the trigger current (usually 1.25 times the rated current), the magnetic force is greater than the spring force, squeezing the iron core into the top of the tube. At this time, the air gap is reduced, causing the magnetic resistance to drop to the minimum, and the center magnetic field strength increases. The armature is therefore attracted, driving the linkage mechanism to operate and the main circuit is disconnected.
When a short circuit or high overload occurs in the main circuit, the iron core of the delay tube moves slowly due to the presence of silicone oil and springs. At this time, the magnetic force generated instantly by the coil is large enough to attract the armature and disconnect the main circuit.

Delay tube structure

The delay tube is filled with silicone oil to control the speed of the core movement.

Different silicone oil viscosities produce different time delay curves

Hydraulic electromagnetic circuit breaker technology

The hydraulic electromagnetic circuit breaker trigger current and ambient temperature curve shows its greatest advantage, namely temperature stability. No temperature derating is required between -40°C and 85°C , while thermal magnetic circuit breakers are more sensitive to temperature.

Advantage:

Minimum power loss at rated current
Performance is not affected by ambient temperature
Operating temperature: -40°C~85°C
Low overload and high precision protection
Resettable
Maximum 6-pole linkage operation
Auxiliary functions and special circuits
Easy to achieve current superposition

shortcoming:

Sensitive to installation location
Slightly expensive

Installation location

From the figure, we can see that because the delay tube uses the principle of force balance to achieve action, the vertical direction of the delay tube will be affected by gravity and needs to be derated accordingly, but no adjustment is required in the horizontal direction.

Overcurrent time characteristics of thermal magnetic circuit breaker

Since thermal-magnetic circuit breakers use the deformation of bimetallic strips to achieve low-overload protection, they are sensitive to ambient temperature, and the corresponding low-overload protection cannot be achieved with high precision.

Overload time characteristics of hydraulic electromagnetic circuit breaker

Since the hydraulic electromagnetic circuit breaker is not affected by the ambient temperature, it can achieve high-precision and fast protection at a low overload of 1.25 times. At the same time, the response time can be adjusted by changing the viscosity of the silicone oil according to actual needs.