T 1241/18 - It is not the person skilled in the art who selects the CPA

 Key points

•  “The selection of an appropriate starting point in the assessment of inventive step is an objective exercise carried out by the deciding body applying the established criteria. ...The board therefore concurs with the findings in T 1450/16 (reasons 2.1.4) and T 0855/15 (reasons 8.2) to the extent that it is not the person skilled in the art that selects a suitable starting point, and in particular the closest prior art document, in the assessment of inventive step. Against this background, in the board's view, the question of who is the competent skilled person is irrelevant at least as regards the selection of a suitable document as a starting point in the assessment of inventive step, because it is not the notional skilled person within the meaning of Article 56 EPC that selects the appropriate starting point.”
• The Board in fact carefully discusses who the skilled person is in a later step of the problem-solution approach. 
• The Board, after carefully reviewing the content of D7: “Although document D7 and the subject-matter of claim 1 are described in terms of different types of power transmission systems (AC, DC), they are thus both concerned with the same subject-matter and serve the same purpose, which clearly qualifies D7 as a suitable starting point in the assessment of inventive step of the subject-matter of claim 1.”
• “The board has therefore arrived at the conclusion that document D7 is a suitable starting point in the assessment of inventive step and the appellant's sole objection under Articles 100(a) and 56 EPC based on this document thus had to be taken into account in the appeal procedure.”
• The Board then formulates the objective technical problem and, before turning to obviousness, discusses who the skilled person is.
• This seems a logical order of steps to me.
• “In view of the objective technical problem, the board considers the competent skilled person in the relevant technical field to be an expert in power transmission systems, who typically is a graduate engineer in electrical engineering or physics with focus on protection systems such as circuit breakers, who has several years of practical experience as a developer in industry. The competent skilled person consequently not only has a broad knowledge in AC power transmission systems but also in (HV)DC transmission systems including circuit breakers for these types of applications. ...  In this context, it is further to be noted that the technical fields of circuit breakers for AC and DC systems are so closely related that a clear boundary between the respective competent notional skilled persons within the meaning of Article 56 EPC cannot be clearly drawn anyway.”
• The Board finds claim 1 to be obvious.

T 1241/18 -

https://www.epo.org/law-practice/case-law-appeals/recent/t181241eu1.html

2. Main request - Inventive step in view of D7

2.1 Suitable starting point

2.1.1 The board does not agree with the respondent that document D7 could not be considered as an appropriate starting point in the assessment of inventive step, because the skilled person of document D7 was competent in the field of AC systems, while the skilled person of the subject-matter of claim 1 was competent in the field of DC systems, which made D7 unsuitable as a starting point in the assessment of inventive step.

2.1.2 The selection of an appropriate starting point in the assessment of inventive step is an objective exercise carried out by the deciding body applying the established criteria. Several criteria have been developed in the case law of the Boards of Appeal in order to establish whether a document could be considered as a suitable starting point in the assessment of inventive step, and in particular whether a document is the "closest prior art" (see Case Law of the Boards of Appeal, 9th edition 2019, I.D.3). The board therefore concurs with the findings in T 1450/16 (reasons 2.1.4) and T 0855/15 (reasons 8.2) to the extent that it is not the person skilled in the art that selects a suitable starting point, and in particular the closest prior art document, in the assessment of inventive step.

Against this background, in the board's view, the question of who is the competent skilled person is irrelevant at least as regards the selection of a suitable document as a starting point in the assessment of inventive step, because it is not the notional skilled person within the meaning of Article 56 EPC that selects the appropriate starting point.

2.1.3 The board considers document D7 to be a suitable starting point in the assessment of inventive step of the subject-matter of claim 1. The subject-matter of claim 1 and document D7 are both concerned with a breaker failure detection system, which relate to the same purpose, namely to increase the stability of a power grid by more reliably interrupting a power transmission circuit during a grid fault event. In both cases, D7 and the invention as defined in claim 1, this is achieved by a breaker failure detection unit that is arranged for retrieving a trip signal used for triggering the circuit breaker, assessing, on the basis of a measured current received from a current sensor, whether the circuit breaker has failed, and sending, if the circuit breaker has failed, a trip signal to an adjacent circuit breaker. This was not disputed by the respondent.

2.1.4 Although document D7 and the subject-matter of claim 1 are described in terms of different types of power transmission systems (AC, DC), they are thus both concerned with the same subject-matter and serve the same purpose, which clearly qualifies D7 as a suitable starting point in the assessment of inventive step of the subject-matter of claim 1.

The board has therefore arrived at the conclusion that document D7 is a suitable starting point in the assessment of inventive step and the appellant's sole objection under Articles 100(a) and 56 EPC based on this document thus had to be taken into account in the appeal procedure.

2.2 Distinguishing features

It was not in dispute between the parties that the subject-matter of claim 1 differs from document D7 only in the features of claim 1, which are specific to the claimed intended use of the breaker failure detection system for an HVDC breaker arranged for interrupting a DC circuit, namely:

- a current sensor being arranged for measuring a current through the DC circuit, and

- at least one inductor connected in series with the DC circuit.

2.3 Objective technical problem

The board agrees with the respondent that the objective technical problem may be considered to be that of how to adapt the breaker failure protection system of D7 to other application scenarios.

2.4 Competent skilled person

2.4.1 In view of the objective technical problem, the board considers the competent skilled person in the relevant technical field to be an expert in power transmission systems, who typically is a graduate engineer in electrical engineering or physics with focus on protection systems such as circuit breakers, who has several years of practical experience as a developer in industry. The competent skilled person consequently not only has a broad knowledge in AC power transmission systems but also in (HV)DC transmission systems including circuit breakers for these types of applications.

2.4.2 In this context, it is to be noted that at the time of publication of D7 (2006), AC transmission systems might have been the dominant technology for large scale power transmission. However, at the effective date of the patent under appeal (14 June 2010), the development of high power semiconductor switches for inverters, such as IGBTs, had already led to an improved practical applicability of HVDC transmission systems. Therefore, while it might be true that AC transmission systems, at the effective date of the patent under appeal, were still the prevailing technology, the skilled person at that time clearly was also aware of developments in the relevant technical field of HVDC transmission systems and had profound knowledge of this technology.

2.4.3 The board agrees with the respondent that document D7 refers to a breaker failure detection system that is obviously foreseen to be used in an AC transmission system. However, the board agrees with the point of view taken by other technical boards of appeal that the skilled person within the meaning of Article 56 EPC usually is the person qualified to solve the objective technical problem rather than the person competent in the field of the claimed invention or the closest prior art (see T 1450/16, reasons 2.1.4 and cited decisions).

The board therefore does not consider the respondent's argument convincing according to which the skilled person in the case at hand is exclusively competent in the field of AC systems. In this context, it is further to be noted that the technical fields of circuit breakers for AC and DC systems are so closely related that a clear boundary between the respective competent notional skilled persons within the meaning of Article 56 EPC cannot be clearly drawn anyway.

2.5 Obviousness

2.5.1 Providing the breaker failure detection system of D7 for an HVDC circuit breaker in order to interrupt a DC circuit, and to thereby implement a current sensor arranged to measure a current in a DC circuit as well as an inductor connected in series to a DC circuit, would have been obvious to the person skilled in the art at the effective date of the patent under appeal.

2.5.2 The skilled person would have considered HVDC circuit breakers arranged to interrupt DC circuits when searching for other areas of application for the breaker failure detection system of D7. In this respect, it is to be noted that, as set out under point 2.4 above, at the effective date of the patent under appeal, the practical applicability of HVDC transmission systems had become widely developed, and these systems were known to be advantageous under certain conditions. Therefore, while it might be true that at the effective date of the patent under appeal, AC transmission was still the prevailing technology, the skilled person at that time clearly was also aware of developments in HVDC power transmission and the board has no doubts that HVDC circuit breakers in a DC circuit therefore would have been considered by the skilled person as a suitable field of application.

2.5.3 Furthermore, the skilled person, when providing the breaker failure detection circuit of D7 for use with an HVDC circuit breaker in a DC circuit, would have been well aware of the necessity to provide an inductor to avoid a sudden change in current through the faulty circuit breaker and the adjacent breakers. There cannot be any doubt that the provision of inductors to limit a current rise is standard practice in DC circuits and therefore does not contribute to an inventive step.

In this respect, it is further to be noted that the skilled person would have recognised immediately that the problems, in particular related to faults in (inductive) harmonic filters, and the provision of an auxiliary signal, as disclosed in D7, section 7.6 on page 13, are entirely AC specific and consequently as not applying to DC circuits. The arguments presented by the respondent in this context, in particular the argument that D7 would have prevented the skilled person from providing an inductor connected in series to the DC circuit, therefore do not convince the board.

The teaching of D4, in particular figure 5 (inductor Ls), is in no way contrary to this understanding. The board considers this document to merely confirm the view that the person skilled in the art would insert an inductor at a suitable position in the DC circuit without involving an inventive step.

In this context, it is further to be noted that claim 1 broadly defines the at least one inductor as being connected in series with the DC circuit, which is an obvious position of the inductor to limit the current flow when it commutates from a faulty circuit breaker to an adjacent circuit breaker during a failure.

2.5.4 Similarly, the provision of a current sensor arranged for measuring a current through the DC circuit is standard practice, and would not have confronted the skilled person with any difficulties when providing the breaker failure detection system as disclosed in D7 for use with an HVDC circuit breaker in a DC related system.

In this respect, the board further notes that D7, especially on page 23, indeed refers to complex current sensing considerations in an AC circuit. However, this would not have prevented the skilled person in any way from implementing the breaker failure detection circuit of D7 for use with an HVDC circuit breaker in a DC circuit. To the contrary, the skilled person would have immediately recognised that the corresponding challenges are specific to AC circuits and therefore do not apply to DC circuits.

2.5.5 The board thus has arrived at the conclusion that the person skilled in the art, taking D7 as a starting point, would have recognised at the effective date of the patent under appeal, in view of the then practical applicability of HVDC power transmission systems and corresponding HVDC circuit breakers, without involving an inventive step, that the objective technical problem was to be solved by providing the breaker failure detection system of D7 for an HVDC circuit breaker to interrupt a DC circuit. The modifications to be made in this context were obvious minor adaptations to the specific application for an HVDC circuit breaker in a DC circuit, which pertained to the common general knowledge of the competent skilled person (see the board's remarks under point 2.4 above).

2.5.6 The board has therefore arrived at the conclusion that the subject-matter of claim 1 as granted is rendered obvious in view of document D7 in combination with the common general knowledge of the competent person skilled in the art. Consequently, the subject-matter of claim 1 does not involve an inventive step and the maintenance of the patent under appeal is thus prejudiced by the ground for opposition under Article 100(a) EPC in combination with Article 56 EPC.