1. NEUTRAL-GROUNDING-RESISTOR MONITOR
SE-330
NEUTRAL-GROUNDING-RESISTOR
MONITOR

2. THE SE-330 NEUTRAL-GROUNDING-RESISTOR MONITOR
The SE-330 is a high performance, microprocessor-based neutral-grounding-resistor monitor that detects NGR failures and ground faults in resistance-grounded systems. The SE-330 measures NGR resistance, current through the NGR, and transformer neutral-to-ground voltage. The SE-330 can be used for alarming or tripping circuits.

3. * NGR monitoring is required by some electrical codes
WHY MONITOR THE NGR?
SE-701 GROUND-FAULT MONITOR
NGR
Failure of the NGR results in an ungrounded system with all of the associated problems such as transient overvoltages.
Ground-fault protection, coordination, and annunciation depend on the integrity of the NGR
Resistors fail open.
We want to monitor the neutral grounding resistor for three reasons:
1. To ensure that the system is grounded, so that it will not suffer the hazards of an ungrounded system (transient overvoltages).
2. To ensure that downstream ground-fault protection equipment will function.
3. NGR monitoring is required in Canada by CAN/CSA-M
Additionally, backup ground-fault protection can be provided in conjunction with NGR monitoring.
* NGR monitoring is required by some electrical codes

4. STARTCO’S APPROACH TO NGR MONITORING
Voltage at the neutral is monitored
*A voltage clamp in the sensing resistor eliminates hazardous voltage levels at the SE-330
CT is used to monitor ground-fault current N R
NGR
Startco’s SE-325 uses a combination of an external sensing resistor and a current transformer (CT) to continuously monitor NGR continuity and ground-fault current.
The SE-325 uses the sensing resistor to monitor NGR resistance and transformer neutral-to-ground voltage to continuously monitor the Neutral Grounding Resistor. It uses the CT to continuously monitor Ground-Fault Current.
NGR resistance: a current is injected into the ‘R’ terminal of the ER-xxx sensing resistor. The sensing resistor forms a series circuit with the NGR, completing the circuit through the ‘G’ terminal. If the SE-325 detects an NGR resistance greater than a threshold value it trips on Resistor Fault. Neutral point voltage elevation trips the unit if the NGR opens with a ground-fault present.
Ground-Fault : The unit will trip on ground-fault when ground-fault current rises above a preset value.
The standard SE-325 latches both ground- and resistor-faults. The SE-325XA offers non-latching operation, normally used in alarm-only systems. G
Continuously monitors resistance using sensing resistor in parallel with NGR

5. NGR SENSING RESISTORS ER-15KV ER-25KV ER-600VC ER-5KV
Startco Engineering manufactures sensing resistors for systems rated up to and including 25 kVac.
External Sensing Resistors: • incorporate a Voltage Clamp
• are installed in parallel with NGR
Sensing Resistor R (k) Max. System Voltage
ER-600VC ,040 Vac
ER-5KV ,330 Vac
ER-15KV ,550 Vac
ER-25KV ,000 Vac
Startco sensing resistors are designed to operate in humid atmospheres. Specifically, 95% relative humidity, non-condensing
Set selector switch on SE-325 face plate to 20 k or 100 k to match sensing resistor resistance rating
ER-5KV

6. NGR SENSING RESISTORS
ER-35KV

7. EXAMPLE- NEUTRAL GROUNDING RESISTOR

8. THE SE-330 NEUTRAL-GROUNDING-RESISTOR MONITOR
Monitors:
NGR resistance
NGR current
Transformer neutral-to-ground voltage
For very high current, or low current Neutral Grounding Resistors
For pulsing ground-fault systems
Detects Open or Shorted NGR’s
SE-325 monitoring functions:
NGR Resistance - with External Sensing Resistor
NGR Current (ground current)
- with CT :5 Current transformer
Transformer Neutral-to-Ground Voltage
- with External Sensing Resistor
The SE-325 is suitable for resistance grounded systems up to and including 25kVac.

9. SE-330 NGR MONITOR - FEATURES
Continuously monitors NGR resistance
Provides Ground-fault protection that ignores harmonics to prevent nusiance tripping
Broad setting ranges
Independent ground-fault and resistor-fault relays for indication and control
Standard local communications
Optional network communications
Pulsing relay to facilitate ground-fault location
4-20 mA Analog Output
Continuous NGR monitoring is a requirement of CSA-M This is a mining standard, but other industries also use it as a guideline.
Ground-fault protection : The SE-325 may be the system’s only ground-fault protection, or may be the back-up to downstream protection devices.
Fail-Safe (UV—undervoltage) operation ensures that the system will not operate if monitor control power is lost. Non-fail-safe (SH—shunt) operation is also selectable.
Red LED’s indicate when a ground-fault or a resistor-fault has caused a trip. There is no confusion as to which condition initiated the trip. Upon either type of trip one set of Form A contacts changes state (operation depends upon selection of UV or SH mode). These contacts are rated 1 mA to 4 A Resistive, 240 Vac or 28 Vdc. They are protected by a 4 A fuse.
The SE-325 does not cause ferroresonance problems. Monitors that use voltage transformers to sense ground-fault current can cause a resonance problem.
Operating temperature range: -40OC to 60OC.
Supply voltage range of -50% to +10%. (previously mentioned)
To test the NGR detection feature of the SE-325 simply disconnect a lead from the sensing resistor (or open a switch installed for this purpose). This causes the detected resistance to go high (), and the unit to trip. The unit’s ground-fault detection feature can be tested with a current source whose output circuit extends through the SE-325’s ground-fault detection CT. (use SE-100T or SE-400 test units.)

10. SE-330 FACE PLATE FUNCTIONS
Status LED’s
Power-On LED
Ground-Fault indication
LED and mechanical flag
Resistor-Fault indication
LED and mechanical flag
GF TRIP LEVEL (% CT RATING):
VN TRIP LEVEL:
Vac or Vac
GF TRIP TIME (s):
adjustable from 0.1 to 10 s
PULSE PERIOD (s):
adjustable from 1 to 3 s
The single-shot Reset button cannot be jammed to provide auto-reset.
A non-latching ground-fault trip option is available (SE-325XA).
Red LED’s indicate the type of trip that has occurred.
RS-232 Local Communication Port:
optional network communications (not shown)
Optical Local Communications Port
Configuration switch cover
Reset Button

11. SE-330 BACKPLATE * The SE-330 can be surface or panel mounted
Unit Healthy Output Contact
Remote Reset
Supply Power
Pulse Enable
Analog Output
Trip/Pulsing Output Contact
Sensing Resistor Terminals
Ground Fault
Indication Contacts
Current Transformer Input:
sensitive, 1A, 5A
Resistor Fault
Indication Contacts
Screw-anchored wire-clamping
plug-in terminal blocks

12. SE-330 SELECTABLE FEATURES
K1 = PULSING
NON-FAIL-SAFE (K1)
NON-LATCHING GF TRIP
NON-LATCHING RF TRIP
100 k
60 Hz
UPGRADE
K1 = TRIP
FAIL-SAFE (K1)
LATCHING GF TRIP
LATCHING RF TRIP
20 k
50 Hz
RUN S1 S2 S3 S4 S5 S6 S7 S8
CALIBRATION PUSH BUTTON

13. SE-330 PULSING CAPABILITY
LOAD 1 4 6
Fault Current pulses with a fixed period
NGR L 22 23 C
NGR N
SE-330 16
Pulsing allows fault to
be located through the
use of a clamp-on meter
Pulse Enable 17
With relay K1 set to pulsing, connect pin 16 & 17
for pulsing operation of output relay K1

14. ALTERNATE PULSING CONFIGURATION
Y-connected transformer
secondary C N
NGR

15. RESISTOR MONITORING WITH A GROUND-FAULT PRESENT
Why measure neutral voltage?
Ground fault provides an
alternate sensing current(IS)
path that bypasses NGR
- SE-330 will trip on
ground fault if IF>GF
for t > GF trip time
-SE-330 will not trip on
resistor fault while fault
current is larger than 5%
of CT rating
If NGR fails, fault current
will diminish, and SE-330 will
indicate a Resistor Fault VN X N
RFAULT
OPEN
NGR R
The SE-325 is sometimes used in alarm-only systems. Alarm- only systems continue to operate with a ground-fault present. If the unit were to only monitor the continuity of the NGR, it could not detect an open NGR with a ground-fault present. This is because a ground-fault provides an alternate path for the NGR sensing current, IS and an open NGR, is not detected. However, the SE-325 must still sense a Resistor Fault in the event that the NGR fails while a ground fault is present. For this reason the SE-325 measures transformer-neutral voltage, VN. During a ground fault, VN is elevated to the system line-to-neutral voltage (This assumes a bolted fault—a high-impedance fault will result in a smaller VN.). With an open NGR, ground-fault current IF will be zero. The SE-325 will trip on Resistor Fault when VN is above Res Trip Level and IF is smaller than GF. If a Ground Fault trip was initiated prior to the NGR failure, then both LED’s will be lit and the relay contact remains in the tripped state.
The Resistor Fault trip circuit is inhibited when ground-fault current is greater than the GF faceplate setting. VN will be at or near system line-to-neutral voltage due to the phase-to-ground fault.
ER-XXXVC G
IS: ALTERNATE PATH
IF: FAULT CURRENT

16. SE-330 TRIP LOGIC-Continuous Monitoring
IF > 5% CT Rating
&
t > ttrip
RNGR > 500 
or 2500  or
VN > VTRIP NO
START
NO TRIP NO
YES
YES
INHIBIT RESISTOR-FAULT TRIP
IF > 5% CT Rating
&
t > ttrip
*RESET: non-latching trips do not require a reset. NO
The SE-325 will indicate a Resistor Fault if the neutral voltage is larger than the Res Trip Level voltage set point and fault current is smaller than the GF current pickup set point.
Ie: If the transformer X0 is at an elevated voltage and there is no fault current then the neutral-grounding resistor is open and the SE-325 indicates a Resistor Fault.
A Resistor Fault will not be indicated when fault current Is larger than the current pickup level. Instead a Ground Fault will be indicated after the GF Trip Time.
YES
GROUND-FAULT
TRIP
RESISTOR-FAULT
TRIP
RESET*
RESET*

17. ARTIFICIAL NEUTRAL SYSTEM
Delta-connected or
wye-connected with
inaccessible-neutral
transformer secondary
ZIGZAG
TRANSFORMER
This view again shows an SE-325 installation, this time in a system that has been retrofitted to a resistance grounded system from an ungrounded one with the addition of a zigzag transformer and Neutral Grounding Resistor. The zigzag transformer creates an artificial neutral and has been added to provide the advantages of a resistance-grounded system, at minimal expense.
A zigzag transformer is a six-winding three-phase transformer that is wye-connected with a pair of series-connected phase-displaced windings symmetrically connected to each phase.
Note that the zigzag transformer power rating need only reflect the prospective ground-fault current and system line-to-neutral voltage. That is, the rating of the NGR. Eg: a 600 V system with a 5A NGR combine for a zigzag transformer rating of only 347 x 5 = 1.7 kVA.
NGR
Startco can provide an entire
Retrofit Package for
Ungrounded Systems

18. NEW SE-330 NGR MONITOR FEATURES
The SE-330 provides new features and improved performance over the SE-325 NGR Monitor:
Increased dc rejection.
Reliable in overhead line applications
Digital Filtering.
Minimizes nuisance trips due to harmonics
Calibrated NGR resistance measurement.
Achieves a lower trip resistance
Separate ground-fault and resistor-fault indication relays.
Used for indication and control
Optional network communications.
Provides information to a distributed control system
Pulsing contacts aid in locating ground faults.
Low and medium voltage alarm-only systems

19. NEW SE-330 NGR MONITOR FEATURES
The SE-330 provides new features and improved performance over the SE-325 NGR Monitor:
4-20 mA analog output
Unit-healthy output contact
Trip flags retain trip indication on power-supply loss
RS-232 and optical local communication ports
provided for program updates and access to parameters

20. SE-330 APPLICATIONS Any resistance-grounded transformer or generator
Pulsing ground-fault location systems
Used in a package with zigzag transformer and Neutral Grounding Resistor to provide monitored resistance grounding for an ungrounded supply
NGR monitoring is mandated in Canada’s mining industry and is recommended in all industries that use resistance grounding
Harmonic-rich applications
Pipeline applications with high current-let-through NGR’s
overhead line applications