GE
Grid Solutions
8 Series
889 Advanced Generator Protection
Technical Note
GE Publication Number: GET-20056
Copyright © 2017 GE Multilin Inc.
Overview
The Multilin 889 is part of the 8 Series platform that provides comprehensive, high
performance protection and control for critical assets in Industrial and utility environments.
Utilizing decades of experience in generator protection, GE has implemented ease-of-use
features, such as single screen setup and condition-based health monitoring and
diagnostics partnered with advanced protection functions providing a comprehensive
solution for Industrial generators.
This paper presents the advanced functionality of several innovative 889 protection
elements including stator differential, 100% stator ground protection, neutral directional
protection, and out-of-step protection.
8 Series 889 Advanced Generator Protection
Technical Note 1
Stator differential (87S) with direction and saturation detection
Differential protection can be considered as the first line of protection for internal stator
phase-to-phase or phase-to-ground faults in induction and synchronous motors.
The 889 stator differential element offers the following distinct features:
Sensitivity to phase-to-phase and phase-to-ground faults
High speed fault detection
Biased differential, allowing different ratios of terminals and neutral CT nominal.
Dual slope characteristic to prevent misoperation caused by spurious differential current during external
faults with a possible CT saturation.
DIR
differential
Operate
OR
Block
Slope 2
SAT
AND Stator
Differential PKP Slope 1
Pickup
DIF
Break 1
Break 2
restraining r
Stator differential logic Stator differential characteristic
Internal phase fault in stator winding scenario External fault with severe CT saturation
8 Series 889 Advanced Generator Protection
2 Technical Note
100% Stator ground protection using the 3rd harmonic voltage
differential (64TN)
100% stator ground protection is easy to apply using the 3rd harmonic voltage differential
(64TN) in conjunction with 59X (auxiliary overvoltage). The 64TN protection function utilizes
the fact that for a fault near the neutral, the 3rd harmonic residual voltage at the terminals of
a machine increases, while the third harmonic voltage at the neutral decreases. The ratio of
the third harmonic residual voltage to the neutral third harmonic may be nearly constant for
all load conditions on a healthy machine without faults. This protection function requires
phase VTs on the terminal side be connected as WYE.
The figure illustrates various protection functions applied for protecting 100% generator
stator winding. It also shows 3rd harmonic voltage distribution over the winding in healthy
condition (no fault on the stator winding).
E3
E3
E3
k
Vn
Va Vb Vc
Vn (3rd)
Pickup
Vn (3rd)V0 (3rd)
Va
and
V0 (3rd) Vb
1 Pickup 3rd
Vn (3rd) Vn (3rd) V0 (3rd) 3V0(3rd) 3V0 Vc
and
Vn (3rd) V0 (3rd) Supervisio n
8 Series 889 Advanced Generator Protection
Technical Note 3
Neutral directional protection (67N) for parallel machine ground
protection coordination
For the application of low impedance grounded parallel generators, the 889 provides neutral
directional (67N) protection function for a secure & selective protection scheme. As
illustrated in figure below, for parallel synchronous generators, a ground fault in any one
machine causes neutral overcurrent (51N) protection to operate in both generators. With
enhanced 67N enabled in both the generators, the faulty generator relay would be identified,
and the healthy machine would continue to run as 67N would not pickup although 51N
indicates a fault condition.
Therefore, 67N in conjunction with 51N in 889 provides secure and selective protection for
parallel operation of synchronous generators connected to the same bus.
8 Series 889 Advanced Generator Protection
4 Technical Note
Out-of-step protection – Easy to apply
The out-of-step element provides an out-of-step (loss-of-synchronism or pole slip) tripping
function for generators. The element is simplified using a single blinder operating
characteristic with an offset mho supervisory. It is easy to apply based on IEEE/ANSI C37.102
guidelines, and an IEEE PES PSRC tutorial on generator protection, which can be accessed at:
http://www.pes-psrc.org/Reports/. Please follow the tutorial for detailed setting calculation
examples.
The purpose of the supervisory mho is to prevent operation on stable swings that pass
through both blinders and outside the mho characteristic.
In addition, the out-of-step tripping feature allows a "MHO EXIT" trip mode to reduce stresses
on the breaker. The figure below illustrates the single blinder characteristic with a
supervisory mho.
X
System
ZmaxS
1.5XT
XFMR θ
XT R
δ
Swing Locus
Gen d
X’d
2X’d
8 Series 889 Advanced Generator Protection
Technical Note 5
For further assistance
For product support, contact the information and call center as follows:
GE Grid Solutions
650 Markland Street
Markham, Ontario
Canada L6C 0M1
Worldwide telephone: +1 905 927 7070
Europe/Middle East/Africa telephone: +34 94 485 88 54
North America toll-free: 1 800 547 8629
Fax: +1 905 927 5098
Worldwide e-mail: multilin.tech@ge.com
Europe e-mail: multilin.tech.euro@ge.com
Website:http://www.gegridsolutions.com/multilin/
8 Series 889 Advanced Generator Protection
6 Technical Note
