Pneumatic Circuit Breaker vs. Spring-Operated Circuit Breaker

A simple answer to a simple question is that one breaker is operated by a compressed gas (could be air or nitrogen), and the other is operated by a charged spring.

I haven't seen a pneumatic breaker in years, and haven't heard of any new models being produced in either HV or LV. I would say the pneumatic breakers are high maintenance compared to spring operated one's which is probably why they're not in common use in the wider world.

Nearly all medium voltage and above circuit breakers on the market today use a spring operating mechanism. However, there are still thousands of pneumatic, hydraulic, and even magnetically operated circuit breakers in use around the world. These "brute force" operators are required in breakers where the insulating medium is oil. Springs came into widespread use with the advent of air, vacuum and gas for insulation and arc quenching. I don't know of a manufacturer who currently offers oil insulation, so the pneumatics, hydraulics and magnetics are also not offered on new units.

SPRING MECHANISM

A spring operated mechanism uses a motor to charge (compress) one or more closing springs, which are held in the compressed condition by a closing latch. When a close signal is provided (through a manual switch or automated control system), a closing solenoid releases the closing latch. The springs push against a mechanical linkage to force the breaker contacts closed. The closing springs also compress the opening springs to prepare for opening the breaker. Once the breaker is closed, a prop latch holds the linkage in position. The motor then compresses the closing springs again to prepare for another closing operation.

When a trip signal is provided, a trip solenoid knocks the prop latch out of position, collapsing the linkage. The opening springs push against the linkage to force the breaker contacts apart. The linkage is designed to return to a condition where it is ready for the breaker to close again.

PNEUMATIC

In a pneumatic system, an air compressor replaces the charging motor, and a piston and storage tank replace the closing springs. The compresssor charges the storage tank, typically to about 100 PSI (700 kPa). The close signal, instead of releasing a latch, opens a valve to allow pressurized air to the piston. The piston pushes against the linkage to force the breaker contacts closed. Again, a prop latch holds the linkage in place, and the piston returns to the ready position.

The trip signal again energizes a trip solenoid to knock the prop latch out from under the linkage, and the opening springs separate the contacts.

HYDRAULIC

Replace the air compressor and tank with a hydraulic pump and accumulator.

MAGNETIC

Replace the air compressor, tank and piston with a large solenoid containing a magnetic ram.

Westinghouse had a large line of oil breakers with pneumatic or hydraulic operators. ABB bought that line, and still supports them. You could probably get operating manuals from them.

Heinemann Electric (who I think may now be owned by Eaton) still makes small low voltage hydraulic breakers, as does Airpax (now called Sensata). The only benefit to hydraulic is that the are virtually impervious to changes in ambient temperature, so they are preferred in applications such as Marine and remote Telecom sites where extremes of temperature may exist.

I haven't seen hydraulic breakers in marine applications, certainly not European built vessels. The reason being oil in flammable, which is another reason why dry type transformers are used at sea.