131 3 SEPED303001EN - 01/2013 Protection functions Thermal overload for transformers ANSI code 49RMS Operation This function is used to protect a transformer against overloads, based on the measurement of the current taken. IEC standard 60076-2 proposes 2 thermal models for evaluating the winding thermal capacity used during an overload, depending on whether the transformer is dry-type or immersed. Taking account of harmonics The equivalent current Ieq measured by the transformer thermal overload protection is the highest of the phase rms currents (the rms current takes account of harmonic numbers up to 13). Taking account of 2 operating conditions The choice between thermal sets 1 and 2 is made by the "switching of thermal settings" logic input. This means you can have thermal set 1 for normal transformer operation and thermal set 2 for unusual transformer operation. Dry-type transformer For dry-type transformers, the thermal model used in the Sepam relay conforms to standard IEC 60076-12 (with 1 time constant). Block diagram DE81253 Dry-type transformer thermal model The thermal limit for dry-type transformers is determined by the thermal limit for insulating components in order to avoid damaging them. The table below defines the maximum permissible temperature and the winding temperature gradient according to the insulation class: Insulation class (°C) Gradient Maximum permissible winding temperature 105 (A) 75 °C (67 °F) 130 °C (266 °F) 120 (E) 90 °C (194 °F) 145 °C (293 °F) 130 (B) 100 °C (212 °F) 155 °C (311 °F) 155 (F) 125 °C (257 °F) 180 °C (356 °F) 180 (H) 150 °C (302 °F) 205 °C (401 °F) 200 170 °C (338 °F) 225 °C (437 °F) 220 190 °C (374 °F) 245 °C (473 °F) The winding maximum permissible thermal capacity used equals: Where: : ambient temperature (rated value equals 20 °C or 68 °F) : temperature gradient at rated current lb : insulating component maximum permissible temperature according to the insulation class Ieq AN / AF Insulation class Switching of thermal settings Insulation class Dry-type transformer thermal model Alarm δθ Trip Inhibition by logic input or TC 20 C Use of temperature sensor + + Max θa I1 rms I2 rms I3 rms Ambient θ sensor θ > θ trip θ > θ alarm Δθ n θ max θ max θ – a θ a Δθ n θ max
22
Embed
Protection functions Thermal overload for transformers ... · 133 3 SEPED303001EN - 01/2013 Protection functions Thermal overload for transformers ANSI code 49RMS Example of a class
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
131
3
SEPED303001EN - 01/2013
Protection functions Thermal overload for transformersANSI code 49RMS
OperationThis function is used to protect a transformer against overloads, based on the
measurement of the current taken.
IEC standard 60076-2 proposes 2 thermal models for evaluating the winding thermal
capacity used during an overload, depending on whether the transformer is dry-type
or immersed.
Taking account of harmonics
The equivalent current Ieq measured by the transformer thermal overload protection
is the highest of the phase rms currents (the rms current takes account of harmonic
numbers up to 13).
Taking account of 2 operating conditions
The choice between thermal sets 1 and 2 is made by the "switching of thermal
settings" logic input. This means you can have thermal set 1 for normal transformer
operation and thermal set 2 for unusual transformer operation.
Dry-type transformerFor dry-type transformers, the thermal model used in the Sepam relay conforms to
standard IEC 60076-12 (with 1 time constant).
Block diagram
DE
81
25
3
Dry-type transformer thermal model
The thermal limit for dry-type transformers is determined by the thermal limit for
insulating components in order to avoid damaging them. The table below defines the
maximum permissible temperature and the winding temperature gradient according
to the insulation class:
Insulation class (°C) Gradient Maximum permissible winding
temperature
105 (A) 75 °C (67 °F) 130 °C (266 °F)
120 (E) 90 °C (194 °F) 145 °C (293 °F)
130 (B) 100 °C (212 °F) 155 °C (311 °F)
155 (F) 125 °C (257 °F) 180 °C (356 °F)
180 (H) 150 °C (302 °F) 205 °C (401 °F)
200 170 °C (338 °F) 225 °C (437 °F)
220 190 °C (374 °F) 245 °C (473 °F)
The winding maximum permissible thermal capacity used equals:
Where:
: ambient temperature (rated value equals 20 °C or 68 °F)
: temperature gradient at rated current lb
: insulating component maximum permissible temperature according to the
insulation class
Ieq
AN / AF Insulation class Switching
of thermal
settings
Insulation
class
Dry-type transformer
thermal model
Alarm
δθ
Trip
Inhibition by
logic input or TC
20 C
Use of
temperature
sensor
+
+Max
θa
I1 rms
I2 rms
I3 rms
Ambient θ sensor
θ > θ trip
θ > θ alarm
∆θnθmax
θmax
θ–a
θa
∆θn
θmax
132
3
SEPED303001EN - 01/2013
Protection functions Thermal overload for transformersANSI code 49RMS
The temperature build-up in the dry-type transformer winding is calculated as
follows:
% Ib:
% Ib:
Where:
: dry-type transformer time constant
: equals 1.6 for transformers with natural cooling (AN)
equals 2 for transformers with forced cooling (AF)
The protection trips when the temperature build-up in the winding reaches
.
Evaluating the time constant
The thermal protection function protects the MV winding as well as the LV winding.
Therefore the time constant corresponds to the lowest value of the MV winding and
LV winding time constants.
The time constant is evaluated, for each winding, according to standard IEC 60076-
12 as follows:
Where:
: total winding loss in Watts
: winding thermal capacity in Watts min, given by the winding material:
b Aluminum: 15 times weight of Al conductor (kg) + 24.5 times weight of epoxy and
other insulating component (kg)
b Copper: 6.42 times weight of Cu conductor (kg) + 24.5 times weight of epoxy and
other insulating component (kg)
: contribution of the core to the thermal capacity used:
b 5 °C (41 °F) for MV winding
b 25 °C (77 °F) for LV winding
δθ
Ieq 5≥ δθn
δθn 1–
∆θnIeq
Ib---------
q
δθn 1–
–⋅ dt
τ------⋅+=
Ieq 5< δθn
δθn 1–
1dt
τ------–
⋅=
τq
δθθ
maxθ–
a
τ
τC ∆θ
nθ
e–( )⋅
Pr-------------------------------------=
PrC
θe
133
3
SEPED303001EN - 01/2013
Protection functions Thermal overload for transformersANSI code 49RMS
Example of a class B dry-type transformer:
Regardless of the winding material, the LV winding has the lowest time constant.
The following graph gives the values of the time constant for different 20 kV / 410
V dry-type transformer power ratings:
DE
81
25
4
20 kV / 410 V dry-type transformer time constant.
Saving the thermal capacity used
On loss of the auxiliary power supply, the winding thermal capacity used is saved.
Operating information
The following information is available to the operator:
b the winding relative thermal capacity used E as a %:
b the time before tripping in minutes (at constant current)
Accounting for ambient temperature
The characteristics of dry-type transformers are defined for an ambient temperature
of 20 °C (68 °F). When the Sepam is equipped with the temperature sensor module
option, the ambient temperature is measured by sensor no. 8 and added to the
winding temperature.
τ
0
10
20
30
40
50
60
70
80
Power (in kVA)
Time constant (in mn)
Cu
Alu
0 500 1000 1500 2000 2500 3000
Ek
100θ
kθa–
∆θn
------------------⋅=
134
3
SEPED303001EN - 01/2013
Protection functions Thermal overload for transformersANSI code 49RMS
CharacteristicsSettings
Measurement origin
Setting range I1, I2, I3 / I'1, I'2, I'3
Choice of transformer or thermal model
Setting range Dry-type transformer
Natural ventilation (AN)
Forced ventilation (AF)
Generic model(1)
Insulation class
Setting range 105 (A)
120 (E)
130 (B)
155 (F)
180 (H)
200
220
Alarm set point ( alarm)
Setting range class 105: 95 °C to 130 °C (203 °F to 266 °F)
class 120: 110 °C to 145 °C (230 °F to 293 °F)
class 130: 120 °C to 155 °C (248 °F to 311 °F)
class 155: 145 °C to 180 °C (293 °F to 356 °F)
class 180: 190 °C to 225 °C (374 °F to 437 °F)
class 220: 210 °C to 245 °C (410 °F to 473 °F)
Resolution 1 °C (1 °F)
Tripping set point ( trip)
Setting range class 105: 95 °C to 130 °C (203 °F to 266 °F)
class 120: 110 °C to 145 °C (230 °F to 293 °F)
class 130: 120 °C to 155 °C (248 °F to 311 °F)
class 155: 145 °C to 180 °C (293 °F to 356 °F)
class 180: 190 °C to 225 °C (374 °F to 437 °F)
class 220: 210 °C to 245 °C (410 °F to 473 °F)
Resolution 1 °C (1 °F)
Transformer time constant ( )
Setting range 1 min to 600 min
Resolution 1 min
Accounting for ambient temperature
Setting range yes / no
Characteristic times
Operating time accuracy ±2 % or ±1 s
Inputs
Designation Syntax Equations Logipam
Reset protection P49RMS_1_101 b b
Inhibit protection P49RMS_1_113 b b
Outputs
Designation Syntax Equations Logipam Matrix
Time-delayed output P49RMS _1_3 b b b
Alarm P49RMS _1_10 b b b
Inhibit closing P49RMS _1_11 b b b
Protection inhibited P49RMS _1_16 b b
Hot state P49RMS _1_18 b b
Thermal overload inhibited P49RMS_1_32 b b
Zero speed P49RMS_1_38 b b
(1) See settings associated with generic thermal overload.
θ
θ
τ
135
3
SEPED303001EN - 01/2013
Protection functions Thermal overload for transformersCode ANSI 49RMS
Immersed transformerFor immersed transformers, the thermal model used in the Sepam relay conforms to
standard IEC 60076-7 (with 2 time constants).
The thermal limit for immersed transformers is determined by the thermal limit for the
oil, to avoid the formation of bubbles that could damage the dielectric strength of the
oil.
Block diagram
DE
81
25
5
Immersed transformer thermal model
The immersed transformer thermal model takes account of thermal exchanges
between the winding and the oil. To this end IEC standard 60076-2 proposes a model
for each of the transformer components:
b a thermal model with 2 time constants for the winding
b a thermal model with 1 time constant for the oil.
The winding thermal model transfer function is as follows:
DE
81
25
6
Where : winding temperature gradient at current Ib
: winding thermal capacity used exponent
: thermal exchange coefficient between the winding and the oil
: multiplying factor applied to the time constants
: winding time constant
: oil time constant
θ > θ trip
θ > θ alarm
Ieq
Use of
temperature
sensor
Max
I1 rms
I2 rms
I3 rms
Winding thermal model
Change of
thermal
settings
Alarm
Trip
Inhibition by
logic input or TC
20°C Oil thermal model
+
+
δθ wdg
θ oil
θ ambient
θ oil
τwdg τoil Transformer
type restricted
Ieq y
Ib
Ieqθ wdg∆
p
k21 -1
+1
k21
k22
− δθ
wdg
∆θenry
κ21κ22τ enr
τ huile
136
3
SEPED303001EN - 01/2013
Protection functions Thermal overload for transformersANSI code 49RMS
IEC standard 60076-7 proposes, depending on the nature of the immersed
transformer, the following values:
Transformer
ONAN (distribution) 1 2 23 °C 1,6 4 min 180 min
ONAN (power) 2 2 26 °C 1,3 10 min 210 min
ONAF 2 2 26 °C 1,3 7 min 150 min
OF 1.3 1 22 °C 1,3 7 min 90 min
OD 1 1 29 °C 2 7 min 90 min
Note: For distribution ONAN and OD transformers, the winding thermal model only reacts with the winding time constant.
When the winding and oil time constants are given by the immersed transformer
manufacturer, the user can enter them in place of the default values proposed by the
standard.
For transformers in which the oil flow can be restricted, exchanges between the
winding and the oil are worse, so the winding thermal capacity used values are
exceeded. In this case coefficient takes the following values:
Transformer Restricted flow
OFF ON
ONAN (power) 2 3
ONAF 2 3
OF 1,3 1,45
Accounting for ambient temperature
The characteristics of immersed transformers are defined for an ambient
temperature of 20 °C (68 °F). When the Sepam is equipped with the temperature
sensor module option, the ambient temperature is measured by sensor no. 8 and
added to the oil temperature rise.
The oil thermal model transfer function is as follows:
DE
81
25
7
Where : oil temperature gradient at current Ib
: ratio between the on-load losses and the no-load losses
: oil thermal capacity used exponent
: multiplying factor applied to the oil time constant
κ21κ22
∆θenr y τ enr τ huile
κ21
Ieq 1 δθ oilθho∆
1 + R
x
∆θhoRx
κ11
137
3
SEPED303001EN - 01/2013
Protection functions Thermal overload for transformersANSI code 49RMS
IEC standard 60076-7 proposes, depending on the nature of the immersed
transformer, the following values:
Transformer
ONAN (distribution) 1 55 °C 0,8 5
ONAN (power) 0,5 52 °C 0,8 6
ONAF 0,5 52 °C 0,8 6
OF 1 56 °C 1 6
OD 1 49 °C 1 6
Taking account of the oil temperature
When the Sepam is equipped with the temperature sensor module option, sensor no.
8 can be assigned to the oil temperature measurement. In this case the oil
temperature measurement is substituted for the oil thermal model. The measured oil
temperature θoil is added to the winding temperature rise.
Saving the thermal capacity used
On loss of the auxiliary power supply, both the winding and oil thermal capacity used
are saved.
Operating information
The following information is available to the operator:
b the time before tripping in minutes (at constant current)
b the relative thermal capacity used of the transformer expressed as a %:
v when the oil temperature is estimated by a calculation: