Electricity + Control January 2015

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Voltage measurements – their significance in motor protection
Unbalanced motor voltages may cause a
current unbalance that increases the op-
erating temperature and energy losses of
the motor.These voltages can magnify the
current unbalance in the stator windings of
a motor as much as 20 times.When the volt-
age unbalance is more than 1 %, de-rating
the motor will help lessen the effects. If the
unbalance exceeds 5 %, it is not advisable
to operate the motor at all, even if it has
been de-rated. When a voltage unbalance
exceeds 3 %, the root cause should be
identified and corrected. For general motor
protection, it is always assumed that the
system voltage is stable.This is due to leg-
islations such as NRS 048. This legislation
is divided into several parts, mainly guid-
ing the quality of the power supply (QOS),
focusing on the voltage parameters, such
as magnitude and dip time.
However, during fault conditions the system
is unstable and it is essential to know the
voltage variation to comprehensively pro-
tect the motor. It is generally known that in a
fixed power system, there is a 1 % increase
in current measurement, therefore a 2 %
increase in voltage. The suddenly fluctuat-
ing voltage also contributes to deteriorating
winding insulation in amotor, thus reducing
the motor life.
NewEle c’s NewCode, KE range and
other motor protection and control relays
measure voltage to ensure comprehensive
motor protection.
Enquiries: Email
ROUND UP EARTHING + LIGHTNING PROTECTION
Powerful combined arrester for telecommunication systems
The new DEHNbox TC 180 from the surge and lightning protec-
tion expert, DEHN, is a compact universal combined arrester in a
surface-mounted plastic enclosure, ideal for protecting information
technology interfaces.The arrester has been optimised for general
installation on telecommunication connections and devices such
as analogue telephones, ISDN and xDSL. Field tests have shown
that the arrester can even be used for high-performance VDSL2
connections. With the DEHNbox, surges are limited to an accept-
able level for the connected terminal equipment without interfering
with the data signal.
This compact, one-size-fits-all, arrester can be easily retrofitted
at any time, thanks to its surface-mounted enclosure which is ide-
ally suited for wall mounting, thus ensuring immediate lightning
and surge protection in existing installations.The cables lead into
the enclosure via an easy-to-install self-sealing rubber grommet,
which not only allows fast and easy installation but also prevents
the penetration of moisture and dust. The cable cores (solid and
flexible with wire end ferrule) and the earthing conductor can be
connected by inserting them into the spring-loaded terminals of
the fast connection system without tools. An additional, separate
terminal allows direct connection to the cable shield of the equipo-
tential bonding system.The DEHNboxTC 180 protects one balanced
data interface (ISDN, analogue telephones, xDSL) and has a high
lightning current discharge capacity of 2,5 kA (10/ 350 µs) per line.
The arrester can be installed in lightning
protection zone boundaries from 0 A to 2
and higher. Its cut-off-frequency of 250 MHz
ensures transmission of high-frequency
signal parts.
Enquiries: Alexis Barwise.Tel.
011 704 1487 or email
Solution for pump motor protection
A range of electronic motor protection and control
relays, especially designed to protect pumps and
motorsfrom a variety of faults associated with this
market is available from NewElec. The entire K
series is aimed at rendering assistance to pump
users and consultants that specify protection
requirements for pumps.
What makes these relays unique is that they
incorporate features such as dry-run protection
and phase reversal protection which are basic
requirements for the protection of pumps. A
model exists for every budget.Themore upmarket
models also include built-in features that allow for
a user-selected pump priming time, as well as a
user-selectable pump operating time slot. Auto-
mated re-start times for dry-run trips are available
together with selectable automatic overload trip
resets. A useful asset on some models permit
the user to measure dry-running conditions by
means of power factor measurements instead of
conventional current measurement so that greater
accuracy can be achieved.
The range includes the most basic features
that need manual adjustments directly by the
user to the more sophisticated that can only be
programmed by the supporting software avoid-
ing possible setting interference by users.These
include the monitoring of statistical information
such as the number of starts, trip faults and pump
efficiency. Motor protection is achieved by the
usual current measurement methods and user-
selectable phase voltage measurements.
Enquiries: Email or
visit
23 January ‘15 Electricity+Control