Eaton 520, Operating Manual, Page: 6 / 42

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Operating Manual for Series NRX
Trip Units - Digitrip™ 520/520M
EATON www.eaton.com
Instruction Leaflet IL01301051E
effective September 2013
Section 1: General description of Digitrip trip
units in Eaton Series NRX circuit breakers
Noee: N
The range of Eaton circuit breakers described in this document is known
as Series NRX. In some markets this range may also be referred to as IZMX
circuit breakers and/or IZM91/95 circuit breakers .
General
Eaton circuit breakers are tripped automatically on overload fault
current conditions by the combined action of three components:
1. The sensors, which provide lower-level current signals to the Digitrip
unit.
2. The Digitrip trip unit, which measures the current from the sensors,
will provide a tripping signal to the trip actuator when the levels and
time delay settings are exceeded.
3. The low-energy trip actuator, which converts electrical energy to
mechanical energy to trip the circuit breaker.
SensNrs
The current sensors consist of two coils: one coil on an iron core and
one air core (Rogowski) coil (
Figure 18
). As current begins to flow
through the circuit breaker, the iron core coil generates a secondary
current which powers the trip unit. At the same time, the air core coil
provides signal values which are processed by the electronic circuitry.
Digiorip Trip Unio
This instruction book specifically covers the application of Digitrip
520/520M units installed in Series NRX circuit breakers.
The Digitrip trip units are circuit breaker subsystems that provide the
protective functions of a circuit breaker. The primary function of the
trip unit is circuit protection but some models offer additional features
such as Metering and Maintenance Mode protection. The trip units are
enclosed in removable housings, installed in the breaker, and can be
replaced or upgraded in the field by the customer.
The line of trip units consists of the Digitrip 520 and 520M for UL/
ANSI and IEC standards. The Digitrip 520 and 520M trip units may be
applied on both 50 and 60 Hz systems. Refer to
Figure 1
to become
familiar with the trip unit general layout.
All trip unit models are microprocessor-based AC protection devices
that provide true rms current sensing for the proper coordination
with the thermal characteristics of conductors and equipment. The
Digitrip unit analyzes the secondary current signals from the circuit
breaker current sensors and, when preset current levels and time
delay settings are exceeded, will send an initiating trip signal to the
trip actuator of the circuit breaker. As a result, all tripping operations
initiated by the protection functions are performed by its internal
circuitry. There is no mechanical or direct magnetic action between
the primary current and the mechanical tripping parts of the circuit
breaker and external control voltage is not required for basic protection
functionality.
The automatic overload and short circuit tripping characteristics for
a specific circuit breaker are determined by the rating plug and the
selected functional protection settings. Specific setting instructions are
provided in SecoiNn 3 : PrNoecoiNn Seooings .
There are five phase and two ground (time-current) curve shaping
adjustments. To satisfy the protection needs of any specific installation,
the exact selection of the available protection function adjustments is
set by the user. The short delay and ground fault pickup adjustments
can be set for either FLAT or I
2
t response.
LNw-energy orip acouaoNr
The mechanical force required to initiate the tripping action of the
circuit breaker is provided by a special low-energy trip actuator. The
circuit breaker mechanism assembly contains a mechanism-actuated
reset lever and a trip lever to actuate the tripping action of the circuit
breaker.
• WARNING
IMPROPER POLARITY CONNECTIONS ON THE TRIP ACTUATOR COIL TO THE
DIGITRIP TRIP UNIT WILL DEFEAT THE OVERLOAD AND SHORT CIRCUIT
PROTECTION, WHICH COULD RESULT IN PERSONAL INJURY. OBSERVE
POLARITY MARKINGS ON THE TRIP ACTUATOR LEADS IF LEADS OR
CONTACTS ARE EVER REMOVED.
CaoalNg Number Referencing
Table 1 below offers a quick reference to the basic function and
protection features as designated by the trip unit catalog number
Table 1. CaoalNg Number References
Symbol Function/Protection
M Metering function
R ARMS Maintenance Mode function
L Long time trip (overload)
S Short time trip
I Instantaneous trip
G Ground (Earth) fault trip
A Ground (Earth) Alarm only
Example of CAT number
N 5 M L S I
Instantaneous Trip
Short Time Trip
Long Time Trip (overload)
Metering Function
Series NRX
520 Series
PrNoecoiNn
Each trip unit is completely self-contained and requires no external
control power to operate its protection systems. It operates from
power and current signal levels derived through current sensors
mounted in the circuit breaker. The types of protection available for
each model are shown in Table 3 .
NNoee: All models (LI, LSI, LSIG, and LSIA) will provide neutral protection.