Overview of MicroLogic Trip Systems
| P Trip Unit with Power Metering |
|
Model |
LS0 |
LI |
LSI |
LSIG |
|---|---|---|---|---|
|
Long-Time + |
Long-Time + |
Long-Time + |
Long-Time + |
|
|
(IEC Rated) |
(UL Listed and ANSI Certified) |
(UL LIsted, ANSI Certified, IEC Rated) |
(UL LIsted, ANSI Certified, IEC Rated) |
|
|
Basic Trip Unit |
2.0 |
3.0 |
5.0 |
— |
|
A Trip Unit |
2.0A |
3.0A |
5.0A |
6.0A |
|
P Trip Unit |
— |
— |
5.0P |
6.0P |
|
H Trip Unit |
— |
— |
5.0H |
6.0H |
All MasterPacT circuit breakers are equipped with the MicroLogic trip system to protect power circuits and loads. MicroLogic trip systems use a set of current transformers (called CTs or sensors) to sense current, a trip unit to evaluate the current, and a tripping solenoid to trip the circuit breaker. Adjustable rotary switches on the trip unit allow the user to set the proper overcurrent or equipment ground-fault current protection required in the electrical system. If current exceeds a set value for longer than its set time delay, the trip system opens the circuit breaker. Alarms may be programmed for remote indications. Measurements of current, voltage, frequency, power, and power quality optimize continuity of service and energy management. MicroLogic trip units can be changed on-site.
Integration of protection functions in the Application Specific Integrated Circuit (ASIC) electronic component used in all MicroLogic trip units guarantees a high degree of reliability and immunity to conducted or radiated disturbances. On MicroLogic P and H trip units, advanced functions are managed by an independent microprocessor.
MasterPacT circuit breakers are shipped with the long-time pickup switch set at 1.0 and all other trip unit adjustments set at their lowest settings. Actual settings required for a specific application must be determined by a qualified consultant or plant engineer. A coordination study is recommended to provide coordination between all circuit breakers in the distribution system.
Thermal Imaging
The thermal imaging function protects the cables or bus bars from overheating in case of low amplitude repetitive faults. Such overheating can be due to repetitive motor starting, fluctuating load, intermittent ground faults, or subsequent closing after a fault.
Traditional electronic protection does not protect against repetitive faults because the duration of each overload above the pickup setting is too short to achieve effective tripping. Nevertheless, each overload involves a temperature rise in the installation, the cumulative effect of which could lead to overheating of the system.
The thermal imaging function remembers and integrates the thermal heating caused by each pickup setting overrun. Before tripping, the integrated heating value will reduce the associated time delay and, therefore, the reaction of the trip unit will be closer to the real heating of the power network system. After tripping, the function will also reduce the time delay when closing the circuit breaker on an overload.