Introduction; Introduction To Pt Unit - Eaton PT 10 Instruction Manual

1. Introduction

1. Introduction Figure 1. The PT Trip Unit.

1.1 Introduction to PT unit

The Power Trip (PT) unit, along with current sensors and a
trip actuator, is the subsystem of a circuit breaker which
provides the protective function. The PT unit analyzes signals
from the current sensors. If current level and time delay
settings are exceeded, then the PT unit will trip the circuit
breaker. The automatic over-load and short circuit tripping
characteristics for a specific circuit breaker are determined
by the current rating and user selected protection settings.
There is no mechanical or direct magnetic action between
the primary current side and the mechanical tripping parts of
the circuit breaker.
The PT unit consists of three modules: a frame module,
a control module and an auxiliary power module. The
control module contains a microcontroller that performs
true RMS current sensing measurements and calculations
for protection. It may be replaced in the field. The frame
module is matched to the ratings of the circuit breaker and
permanently attached to the circuit breaker frame. It should
not be removed or exchanged. The auxiliary power module is
EASY400-POW.
PT UNIT USER MANUAL APRIL 2023 www.eaton.com.cn 1